---
layout: "default"
title: "Collection"
description: "Swift documentation for 'Collection': A sequence whose elements can be traversed multiple times,."
keywords: "Collection,protocol,swift,documentation,distance,dropFirst,dropLast,filter,forEach,formIndex,formIndex,formIndex,index,index,index,makeIterator,map,prefix,prefix,prefix,split,suffix,suffix,count,first,indices,isEmpty,endIndex,startIndex,underestimatedCount,IndexDistance,Iterator,SubSequence,Indices,Index"
root: "/v3.0"
---

<div class="intro-declaration"><code class="language-swift">protocol Collection</code></div>

<div class="discussion comment">
    <p>A sequence whose elements can be traversed multiple times,
nondestructively, and accessed by indexed subscript.</p>

<p>Collections are used extensively throughout the standard library. When you
use arrays, dictionaries, views of a string&#39;s contents and other types,
you benefit from the operations that the <code>Collection</code> protocol declares
and implements.</p>

<p>In addition to the methods that collections inherit from the <code>Sequence</code>
protocol, you gain access to methods that depend on accessing an element
at a specific position when using a collection.</p>

<p>For example, if you want to print only the first word in a string, search
for the index of the first space and then create a subsequence up to that
position.</p>

<pre><code class="language-swift">let text = &quot;Buffalo buffalo buffalo buffalo.&quot;
if let firstSpace = text.characters.index(of: &quot; &quot;) {
    print(String(text.characters.prefix(upTo: firstSpace)))
}
// Prints &quot;Buffalo&quot;</code></pre>

<p>The <code>firstSpace</code> constant is an index into the <code>text.characters</code>
collection. <code>firstSpace</code> is the position of the first space in the
collection. You can store indices in variables, and pass them to
collection algorithms or use them later to access the corresponding
element. In the example above, <code>firstSpace</code> is used to extract the prefix
that contains elements up to that index.</p>

<p>You can pass only valid indices to collection operations. You can find a
complete set of a collection&#39;s valid indices by starting with the
collection&#39;s <code>startIndex</code> property and finding every successor up to, and
including, the <code>endIndex</code> property. All other values of the <code>Index</code> type,
such as the <code>startIndex</code> property of a different collection, are invalid
indices for this collection.</p>

<p>Saved indices may become invalid as a result of mutating operations; for
more information about index invalidation in mutable collections, see the
reference for the <code>MutableCollection</code> and <code>RangeReplaceableCollection</code>
protocols, as well as for the specific type you&#39;re using.</p>

<h1>Accessing Individual Elements</h1>

<p>You can access an element of a collection through its subscript with any
valid index except the collection&#39;s <code>endIndex</code> property, a &quot;past the end&quot;
index that does not correspond with any element of the collection.</p>

<p>Here&#39;s an example of accessing the first character in a string through its
subscript:</p>

<pre><code class="language-swift">let firstChar = text.characters[text.characters.startIndex]
print(firstChar)
// Prints &quot;B&quot;</code></pre>

<p>The <code>Collection</code> protocol declares and provides default implementations for
many operations that depend on elements being accessible by their
subscript. For example, you can also access the first character of <code>text</code>
using the <code>first</code> property, which has the value of the first element of
the collection, or <code>nil</code> if the collection is empty.</p>

<pre><code class="language-swift">print(text.characters.first)
// Prints &quot;Optional(&quot;B&quot;)&quot;</code></pre>

<h1>Traversing a Collection</h1>

<p>Although a sequence can be consumed as it is traversed, a collection is
guaranteed to be multipass: Any element may be repeatedly accessed by
saving its index. Moreover, a collection&#39;s indices form a finite range of
the positions of the collection&#39;s elements. This guarantees the safety of
operations that depend on a sequence being finite, such as checking to see
whether a collection contains an element.</p>

<p>Iterating over the elements of a collection by their positions yields the
same elements in the same order as iterating over that collection using
its iterator. This example demonstrates that the <code>characters</code> view of a
string returns the same characters in the same order whether the view&#39;s
indices or the view itself is being iterated.</p>

<pre><code class="language-swift">let word = &quot;Swift&quot;
for character in word.characters {
    print(character)
}
// Prints &quot;S&quot;
// Prints &quot;w&quot;
// Prints &quot;i&quot;
// Prints &quot;f&quot;
// Prints &quot;t&quot;

for i in word.characters.indices {
    print(word.characters[i])
}
// Prints &quot;S&quot;
// Prints &quot;w&quot;
// Prints &quot;i&quot;
// Prints &quot;f&quot;
// Prints &quot;t&quot;</code></pre>

<h1>Conforming to the Collection Protocol</h1>

<p>If you create a custom sequence that can provide repeated access to its
elements, make sure that its type conforms to the <code>Collection</code> protocol in
order to give a more useful and more efficient interface for sequence and
collection operations. To add <code>Collection</code> conformance to your type, you
must declare at least the four following requirements:</p>

<ul><li>the <code>startIndex</code> and <code>endIndex</code> properties,</li><li>a subscript that provides at least read-only access to your type&#39;s
elements, and</li><li>the <code>index(after:)</code> method for advancing an index into your collection.</li></ul>

<h1>Expected Performance</h1>

<p>Types that conform to <code>Collection</code> are expected to provide the <code>startIndex</code>
and <code>endIndex</code> properties and subscript access to elements as O(1)
operations. Types that are not able to guarantee that expected performance
must document the departure, because many collection operations depend on
O(1) subscripting performance for their own performance guarantees.</p>

<p>The performance of some collection operations depends on the type of index
that the collection provides. For example, a random-access collection,
which can measure the distance between two indices in O(1) time, will be
able to calculate its <code>count</code> property in O(1) time. Conversely, because a
forward or bidirectional collection must traverse the entire collection to
count the number of contained elements, accessing its <code>count</code> property is
an O(<em>n</em>) operation.</p>
</div>

<table class="standard">
<tr>
<th id="inheritance">Inheritance</th>
<td>
<code class="inherits">Indexable, IndexableBase, Sequence</code>
<span class="viz"><a href="hierarchy/">View Protocol Hierarchy &rarr;</a></span>
</td>
</tr>

<tr>
<th id="aliases">Associated Types</th>
<td>
<span id="aliasesmark"></span>
<div class="declaration">
<code class="language-swift">IndexDistance : SignedInteger = Int</code>
<div class="comment">
    <p>A type that can represent the number of steps between a pair of
indices.</p>
</div>
</div>
<div class="declaration">
<code class="language-swift">Iterator : IteratorProtocol = IndexingIterator&lt;Self&gt;</code>
<div class="comment">
    <p>A type that provides the collection&#39;s iteration interface and
encapsulates its iteration state.</p>

<p>By default, a collection conforms to the <code>Sequence</code> protocol by
supplying a <code>IndexingIterator</code> as its associated <code>Iterator</code>
type.</p>
</div>
</div>
<div class="declaration">
<code class="language-swift">SubSequence : IndexableBase, Sequence = Slice&lt;Self&gt;</code>
<div class="comment">
    <p>A sequence that represents a contiguous subrange of the collection&#39;s
elements.</p>

<p>This associated type appears as a requirement in the <code>Sequence</code>
protocol, but it is restated here with stricter constraints. In a
collection, the subsequence should also conform to <code>Collection</code>.</p>
</div>
</div>
<div class="declaration">
<code class="language-swift">Indices : IndexableBase, Sequence = DefaultIndices&lt;Self&gt;</code>
<div class="comment">
    <p>A type that can represent the indices that are valid for subscripting the
collection, in ascending order.</p>
</div>
</div>
<div class="declaration inherited">
<code class="language-swift">Index : Comparable</code>
<div class="comment">
    <p>A type that represents a position in the collection.</p>

<p>Valid indices consist of the position of every element and a
&quot;past the end&quot; position that&#39;s not valid for use as a subscript
argument.</p>

<p><strong>See Also:</strong> endIndex</p>
</div>
</div>
</td>
</tr>


<tr>
<th>Import</th>
<td><code class="language-swift">import Swift</code></td>
</tr>

</table>




<h3>Instance Variables</h3>
<div class="declaration" id="var-count_-self-indexdistance">
<a class="toggle-link" data-toggle="collapse" href="#comment-var-count_-self-indexdistance">var count: Self.IndexDistance</a><div class="comment collapse" id="comment-var-count_-self-indexdistance"><div class="p">
    <p>The number of elements in the collection.</p>

<p><strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the length
  of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var count: Self.IndexDistance { get }</code>

    </div></div>
</div>
<div class="declaration" id="var-first_-self-iterator-element">
<a class="toggle-link" data-toggle="collapse" href="#comment-var-first_-self-iterator-element">var first: Self.Iterator.Element?</a><div class="comment collapse" id="comment-var-first_-self-iterator-element"><div class="p">
    <p>The first element of the collection.</p>

<p>If the collection is empty, the value of this property is <code>nil</code>.</p>

<pre><code class="language-swift">let numbers = [10, 20, 30, 40, 50]
if let firstNumber = numbers.first {
    print(firstNumber)
}
// Prints &quot;10&quot;</code></pre>

    <h4>Declaration</h4>    
    <code class="language-swift">var first: Self.Iterator.Element? { get }</code>

    </div></div>
</div>
<div class="declaration" id="var-indices_-self-indices">
<a class="toggle-link" data-toggle="collapse" href="#comment-var-indices_-self-indices">var indices: Self.Indices</a> <span class="required">Required</span><div class="comment collapse" id="comment-var-indices_-self-indices"><div class="p">
    <p>The indices that are valid for subscripting the collection, in ascending
order.</p>

<p>A collection&#39;s <code>indices</code> property can hold a strong reference to the
collection itself, causing the collection to be non-uniquely referenced.
If you mutate the collection while iterating over its indices, a strong
reference can cause an unexpected copy of the collection. To avoid the
unexpected copy, use the <code>index(after:)</code> method starting with
<code>startIndex</code> to produce indices instead.</p>

<pre><code class="language-swift">var c = MyFancyCollection([10, 20, 30, 40, 50])
var i = c.startIndex
while i != c.endIndex {
    c[i] /= 5
    i = c.index(after: i)
}
// c == MyFancyCollection([2, 4, 6, 8, 10])</code></pre>

    <h4>Declaration</h4>    
    <code class="language-swift">var indices: Self.Indices { get }</code>

    </div></div>
</div>
<div class="declaration" id="var-isempty_-bool">
<a class="toggle-link" data-toggle="collapse" href="#comment-var-isempty_-bool">var isEmpty: Bool</a><div class="comment collapse" id="comment-var-isempty_-bool"><div class="p">
    <p>A Boolean value indicating whether the collection is empty.</p>

<p>When you need to check whether your collection is empty, use the
<code>isEmpty</code> property instead of checking that the <code>count</code> property is
equal to zero. For collections that don&#39;t conform to
<code>RandomAccessCollection</code>, accessing the <code>count</code> property iterates
through the elements of the collection.</p>

<pre><code class="language-swift">let horseName = &quot;Silver&quot;
if horseName.characters.isEmpty {
    print(&quot;I&#39;ve been through the desert on a horse with no name.&quot;)
} else {
    print(&quot;Hi ho, \(horseName)!&quot;)
}
// Prints &quot;Hi ho, Silver!&quot;)</code></pre>

<p><strong>Complexity:</strong> O(1)</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var isEmpty: Bool { get }</code>

    </div></div>
</div>
<div class="declaration inherited" id="var-endindex_-self-index">
<a class="toggle-link" data-toggle="collapse" href="#comment-var-endindex_-self-index">var endIndex: Self.Index</a> <span class="required">Required</span><div class="comment collapse" id="comment-var-endindex_-self-index"><div class="p">
    <p>The collection&#39;s &quot;past the end&quot; position---that is, the position one
greater than the last valid subscript argument.</p>

<p>When you need a range that includes the last element of a collection, use
the half-open range operator (<code>..&lt;</code>) with <code>endIndex</code>. The <code>..&lt;</code> operator
creates a range that doesn&#39;t include the upper bound, so it&#39;s always
safe to use with <code>endIndex</code>. For example:</p>

<pre><code class="language-swift">let numbers = [10, 20, 30, 40, 50]
if let index = numbers.index(of: 30) {
    print(numbers[index ..&lt; numbers.endIndex])
}
// Prints &quot;[30, 40, 50]&quot;</code></pre>

<p>If the collection is empty, <code>endIndex</code> is equal to <code>startIndex</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var endIndex: Self.Index { get }</code>

        <h4>Declared In</h4>
            <a href="../../protocol/IndexableBase/"><code>IndexableBase</code></a>
        </div></div>
</div>
<div class="declaration inherited" id="var-startindex_-self-index">
<a class="toggle-link" data-toggle="collapse" href="#comment-var-startindex_-self-index">var startIndex: Self.Index</a> <span class="required">Required</span><div class="comment collapse" id="comment-var-startindex_-self-index"><div class="p">
    <p>The position of the first element in a nonempty collection.</p>

<p>If the collection is empty, <code>startIndex</code> is equal to <code>endIndex</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var startIndex: Self.Index { get }</code>

        <h4>Declared In</h4>
            <a href="../../protocol/IndexableBase/"><code>IndexableBase</code></a>
        </div></div>
</div>
<div class="declaration inherited" id="var-underestimatedcount_-int">
<a class="toggle-link" data-toggle="collapse" href="#comment-var-underestimatedcount_-int">var underestimatedCount: Int</a><div class="comment collapse" id="comment-var-underestimatedcount_-int"><div class="p">
    <p>A value less than or equal to the number of elements in
the sequence, calculated nondestructively.</p>

<p><strong>Complexity:</strong> O(1)</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var underestimatedCount: Int { get }</code>

        <h4>Declared In</h4>
            <a href="../../protocol/Sequence/"><code>Sequence</code></a>
        </div></div>
</div>

<h3>Subscripts</h3>
<div class="declaration" id="subscript-subscript_-self-index">
<a class="toggle-link" data-toggle="collapse" href="#comment-subscript-subscript_-self-index">subscript(_: Self.Index)</a> <span class="required">Required</span>
<div class="comment collapse" id="comment-subscript-subscript_-self-index"><div class="p">
    <p>Accesses the element at the specified position.</p>

<p>The following example accesses an element of an array through its
subscript to print its value:</p>

<pre><code class="language-swift">var streets = [&quot;Adams&quot;, &quot;Bryant&quot;, &quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]
print(streets[1])
// Prints &quot;Bryant&quot;</code></pre>

<p>You can subscript a collection with any valid index other than the
collection&#39;s end index. The end index refers to the position one past
the last element of a collection, so it doesn&#39;t correspond with an
element.</p>

<p><strong><code>position</code>:</strong>  The position of the element to access. <code>position</code>
  must be a valid index of the collection that is not equal to the
  <code>endIndex</code> property.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">subscript(position: Self.Index) -&gt; Self.Iterator.Element { get }</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Collection/"><code>Collection</code></a>,    <a href="../../protocol/IndexableBase/"><code>IndexableBase</code></a>    
</div></div>
</div>
<div class="declaration" id="subscript-subscript_-range-self-index">
<a class="toggle-link" data-toggle="collapse" href="#comment-subscript-subscript_-range-self-index">subscript(_: Range&lt;Self.Index&gt;)</a> <span class="required">Required</span>
<div class="comment collapse" id="comment-subscript-subscript_-range-self-index"><div class="p">
    <p>Accesses a contiguous subrange of the collection&#39;s elements.</p>

<p>The accessed slice uses the same indices for the same elements as the
original collection uses. Always use the slice&#39;s <code>startIndex</code> property
instead of assuming that its indices start at a particular value.</p>

<p>This example demonstrates getting a slice of an array of strings, finding
the index of one of the strings in the slice, and then using that index
in the original array.</p>

<pre><code class="language-swift">let streets = [&quot;Adams&quot;, &quot;Bryant&quot;, &quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]
let streetsSlice = streets[2 ..&lt; streets.endIndex]
print(streetsSlice)
// Prints &quot;[&quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]&quot;

let index = streetsSlice.index(of: &quot;Evarts&quot;)    // 4
print(streets[index!])
// Prints &quot;Evarts&quot;</code></pre>

<p><strong><code>bounds</code>:</strong>  A range of the collection&#39;s indices. The bounds of
  the range must be valid indices of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">subscript(bounds: Range&lt;Self.Index&gt;) -&gt; Self.SubSequence { get }</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Collection/"><code>Collection</code></a>,    <a href="../../protocol/IndexableBase/"><code>IndexableBase</code></a>    
</div></div>
</div>


<h3>Instance Methods</h3>
<div class="declaration" id="func-distance-from_to_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-distance-from_to_">func distance(<wbr>from:<wbr>to:)</a>
        
<div class="comment collapse" id="comment-func-distance-from_to_"><div class="p">
    <p>Returns the distance between two indices.</p>

<p>Unless the collection conforms to the <code>BidirectionalCollection</code> protocol,
<code>start</code> must be less than or equal to <code>end</code>.</p>

<p><strong>Parameters:</strong>
  <strong>start:</strong> A valid index of the collection.
  <strong>end:</strong> Another valid index of the collection. If <code>end</code> is equal to
    <code>start</code>, the result is zero.
<strong>Returns:</strong> The distance between <code>start</code> and <code>end</code>. The result can be
  negative only if the collection conforms to the
  <code>BidirectionalCollection</code> protocol.</p>

<p><strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the
  resulting distance.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func distance(from start: Self.Index, to end: Self.Index) -&gt; Self.IndexDistance</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Collection/"><code>Collection</code></a>,    <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-dropfirst_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-dropfirst_">func dropFirst(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-dropfirst_"><div class="p">
    <p>Returns a subsequence containing all but the given number of initial
elements.</p>

<p>If the number of elements to drop exceeds the number of elements in
the sequence, the result is an empty subsequence.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.dropFirst(2))
// Prints &quot;[3, 4, 5]&quot;
print(numbers.dropFirst(10))
// Prints &quot;[]&quot;</code></pre>

<p><strong><code>n</code>:</strong>  The number of elements to drop from the beginning of
  the sequence. <code>n</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence starting after the specified number of
  elements.</p>

<p><strong>Complexity:</strong> O(<em>n</em>), where <em>n</em> is the number of elements to drop from
  the beginning of the sequence.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func dropFirst(_ n: Int) -&gt; Self.SubSequence</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-droplast_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-droplast_">func dropLast(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-droplast_"><div class="p">
    <p>Returns a subsequence containing all but the specified number of final
elements.</p>

<p>The sequence must be finite. If the number of elements to drop exceeds
the number of elements in the sequence, the result is an empty
subsequence.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.dropLast(2))
// Prints &quot;[1, 2, 3]&quot;
print(numbers.dropLast(10))
// Prints &quot;[]&quot;</code></pre>

<p><strong><code>n</code>:</strong>  The number of elements to drop off the end of the
  sequence. <code>n</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence leaving off the specified number of elements.</p>

<p><strong>Complexity:</strong> O(<em>n</em>), where <em>n</em> is the length of the sequence.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func dropLast(_ n: Int) -&gt; Self.SubSequence</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-filter_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-filter_">func filter(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-filter_"><div class="p">
    <p>Returns an array containing, in order, the elements of the sequence
that satisfy the given predicate.</p>

<p>In this example, <code>filter</code> is used to include only names shorter than
five characters.</p>

<pre><code class="language-swift">let cast = [&quot;Vivien&quot;, &quot;Marlon&quot;, &quot;Kim&quot;, &quot;Karl&quot;]
let shortNames = cast.filter { $0.characters.count &lt; 5 }
print(shortNames)
// Prints &quot;[&quot;Kim&quot;, &quot;Karl&quot;]&quot;</code></pre>

<p><strong><code>isIncluded</code>:</strong>  A closure that takes an element of the
  sequence as its argument and returns a Boolean value indicating
  whether the element should be included in the returned array.
<strong>Returns:</strong> An array of the elements that <code>includeElement</code> allowed.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func filter(_ isIncluded: (Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; [Self.Iterator.Element]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-foreach_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-foreach_">func forEach(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-foreach_"><div class="p">
    <p>Calls the given closure on each element in the sequence in the same order
as a <code>for</code>-<code>in</code> loop.</p>

<p>The two loops in the following example produce the same output:</p>

<pre><code class="language-swift">let numberWords = [&quot;one&quot;, &quot;two&quot;, &quot;three&quot;]
for word in numberWords {
    print(word)
}
// Prints &quot;one&quot;
// Prints &quot;two&quot;
// Prints &quot;three&quot;

numberWords.forEach { word in
    print(word)
}
// Same as above</code></pre>

<p>Using the <code>forEach</code> method is distinct from a <code>for</code>-<code>in</code> loop in two
important ways:</p>

<ol><li>You cannot use a <code>break</code> or <code>continue</code> statement to exit the current
call of the <code>body</code> closure or skip subsequent calls.</li><li>Using the <code>return</code> statement in the <code>body</code> closure will exit only from
the current call to <code>body</code>, not from any outer scope, and won&#39;t skip
subsequent calls.</li></ol>

<p><strong><code>body</code>:</strong>  A closure that takes an element of the sequence as a
  parameter.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func forEach(_ body: (Self.Iterator.Element) throws -&gt; Swift.Void) rethrows</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-formindex_offsetby_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-formindex_offsetby_">func formIndex(<wbr>_:<wbr>offsetBy:)</a>
        
<div class="comment collapse" id="comment-func-formindex_offsetby_"><div class="p">
    <p>Offsets the given index by the specified distance.</p>

<p>The value passed as <code>n</code> must not offset <code>i</code> beyond the <code>endIndex</code> or
before the <code>startIndex</code> of this collection.</p>

<p><strong>Parameters:</strong>
  <strong>i:</strong> A valid index of the collection.
  <strong>n:</strong> The distance to offset <code>i</code>. <code>n</code> must not be negative unless the
    collection conforms to the <code>BidirectionalCollection</code> protocol.</p>

<p><strong>See Also:</strong> <code>index(_:offsetBy:)</code>, <code>formIndex(_:offsetBy:limitedBy:)</code>
<strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the absolute
  value of <code>n</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func formIndex(_ i: inout Self.Index, offsetBy n: Self.IndexDistance)</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-formindex_offsetby_limitedby_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-formindex_offsetby_limitedby_">func formIndex(<wbr>_:<wbr>offsetBy:<wbr>limitedBy:)</a>
        
<div class="comment collapse" id="comment-func-formindex_offsetby_limitedby_"><div class="p">
    <p>Offsets the given index by the specified distance, or so that it equals
the given limiting index.</p>

<p>The value passed as <code>n</code> must not offset <code>i</code> beyond the <code>endIndex</code> or
before the <code>startIndex</code> of this collection, unless the index passed as
<code>limit</code> prevents offsetting beyond those bounds.</p>

<p><strong>Parameters:</strong>
  <strong>i:</strong> A valid index of the collection.
  <strong>n:</strong> The distance to offset <code>i</code>. <code>n</code> must not be negative unless the
    collection conforms to the <code>BidirectionalCollection</code> protocol.
<strong>Returns:</strong> <code>true</code> if <code>i</code> has been offset by exactly <code>n</code> steps without
  going beyond <code>limit</code>; otherwise, <code>false</code>. When the return value is
  <code>false</code>, the value of <code>i</code> is equal to <code>limit</code>.</p>

<p><strong>See Also:</strong> <code>index(_:offsetBy:)</code>, <code>formIndex(_:offsetBy:limitedBy:)</code>
<strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the absolute
  value of <code>n</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func formIndex(_ i: inout Self.Index, offsetBy n: Self.IndexDistance, limitedBy limit: Self.Index) -&gt; Bool</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-formindex-after_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-formindex-after_">func formIndex(<wbr>after:)</a>
        
<div class="comment collapse" id="comment-func-formindex-after_"><div class="p">
    <p>Replaces the given index with its successor.</p>

<p><strong><code>i</code>:</strong>  A valid index of the collection. <code>i</code> must be less than
  <code>endIndex</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func formIndex(after i: inout Self.Index)</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/IndexableBase/"><code>IndexableBase</code></a>    
</div></div>
</div>
<div class="declaration" id="func-index_offsetby_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-index_offsetby_">func index(<wbr>_:<wbr>offsetBy:)</a>
        
<div class="comment collapse" id="comment-func-index_offsetby_"><div class="p">
    <p>Returns an index that is the specified distance from the given index.</p>

<p>The following example obtains an index advanced four positions from a
string&#39;s starting index and then prints the character at that position.</p>

<pre><code class="language-swift">let s = &quot;Swift&quot;
let i = s.index(s.startIndex, offsetBy: 4)
print(s[i])
// Prints &quot;t&quot;</code></pre>

<p>The value passed as <code>n</code> must not offset <code>i</code> beyond the <code>endIndex</code> or
before the <code>startIndex</code> of this collection.</p>

<p><strong>Parameters:</strong>
  <strong>i:</strong> A valid index of the collection.
  <strong>n:</strong> The distance to offset <code>i</code>. <code>n</code> must not be negative unless the
    collection conforms to the <code>BidirectionalCollection</code> protocol.
<strong>Returns:</strong> An index offset by <code>n</code> from the index <code>i</code>. If <code>n</code> is positive,
  this is the same value as the result of <code>n</code> calls to <code>index(after:)</code>.
  If <code>n</code> is negative, this is the same value as the result of <code>-n</code> calls
  to <code>index(before:)</code>.</p>

<p><strong>See Also:</strong> <code>index(_:offsetBy:limitedBy:)</code>, <code>formIndex(_:offsetBy:)</code>
<strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the absolute
  value of <code>n</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func index(_ i: Self.Index, offsetBy n: Self.IndexDistance) -&gt; Self.Index</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Collection/"><code>Collection</code></a>,    <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration" id="func-index_offsetby_limitedby_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-index_offsetby_limitedby_">func index(<wbr>_:<wbr>offsetBy:<wbr>limitedBy:)</a>
        
<div class="comment collapse" id="comment-func-index_offsetby_limitedby_"><div class="p">
    <p>Returns an index that is the specified distance from the given index,
unless that distance is beyond a given limiting index.</p>

<p>The following example obtains an index advanced four positions from a
string&#39;s starting index and then prints the character at that position.
The operation doesn&#39;t require going beyond the limiting <code>s.endIndex</code>
value, so it succeeds.</p>

<pre><code class="language-swift">let s = &quot;Swift&quot;
if let i = s.index(s.startIndex, offsetBy: 4, limitedBy: s.endIndex) {
    print(s[i])
}
// Prints &quot;t&quot;</code></pre>

<p>The next example attempts to retrieve an index six positions from
<code>s.startIndex</code> but fails, because that distance is beyond the index
passed as <code>limit</code>.</p>

<pre><code class="language-swift">let j = s.index(s.startIndex, offsetBy: 6, limitedBy: s.endIndex)
print(j)
// Prints &quot;nil&quot;</code></pre>

<p>The value passed as <code>n</code> must not offset <code>i</code> beyond the <code>endIndex</code> or
before the <code>startIndex</code> of this collection, unless the index passed as
<code>limit</code> prevents offsetting beyond those bounds.</p>

<p><strong>Parameters:</strong>
  <strong>i:</strong> A valid index of the collection.
  <strong>n:</strong> The distance to offset <code>i</code>. <code>n</code> must not be negative unless the
    collection conforms to the <code>BidirectionalCollection</code> protocol.
  <strong>limit:</strong> A valid index of the collection to use as a limit. If <code>n &gt; 0</code>,
    a limit that is less than <code>i</code> has no effect. Likewise, if <code>n &lt; 0</code>, a
    limit that is greater than <code>i</code> has no effect.
<strong>Returns:</strong> An index offset by <code>n</code> from the index <code>i</code>, unless that index
  would be beyond <code>limit</code> in the direction of movement. In that case,
  the method returns <code>nil</code>.</p>

<p><strong>See Also:</strong> <code>index(_:offsetBy:)</code>, <code>formIndex(_:offsetBy:limitedBy:)</code>
<strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the absolute
  value of <code>n</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func index(_ i: Self.Index, offsetBy n: Self.IndexDistance, limitedBy limit: Self.Index) -&gt; Self.Index?</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Collection/"><code>Collection</code></a>,    <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-index-after_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-index-after_">func index(<wbr>after:)</a>
     <span class="required">Required</span>    
<div class="comment collapse" id="comment-func-index-after_"><div class="p">
    <p>Returns the position immediately after the given index.</p>

<p><strong><code>i</code>:</strong>  A valid index of the collection. <code>i</code> must be less than
  <code>endIndex</code>.
<strong>Returns:</strong> The index value immediately after <code>i</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func index(after i: Self.Index) -&gt; Self.Index</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/IndexableBase/"><code>IndexableBase</code></a>    
</div></div>
</div>
<div class="declaration" id="func-makeiterator">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-makeiterator">func makeIterator()</a>
     <span class="required">Required</span>    
<div class="comment collapse" id="comment-func-makeiterator"><div class="p">
    <p>Returns an iterator over the elements of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func makeIterator() -&gt; Self.Iterator</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Collection/"><code>Collection</code></a>,    <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-map_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-map_">func map(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-map_"><div class="p">
    <p>Returns an array containing the results of mapping the given closure
over the sequence&#39;s elements.</p>

<p>In this example, <code>map</code> is used first to convert the names in the array
to lowercase strings and then to count their characters.</p>

<pre><code class="language-swift">let cast = [&quot;Vivien&quot;, &quot;Marlon&quot;, &quot;Kim&quot;, &quot;Karl&quot;]
let lowercaseNames = cast.map { $0.lowercaseString }
// &#39;lowercaseNames&#39; == [&quot;vivien&quot;, &quot;marlon&quot;, &quot;kim&quot;, &quot;karl&quot;]
let letterCounts = cast.map { $0.characters.count }
// &#39;letterCounts&#39; == [6, 6, 3, 4]</code></pre>

<p><strong><code>transform</code>:</strong>  A mapping closure. <code>transform</code> accepts an
  element of this sequence as its parameter and returns a transformed
  value of the same or of a different type.
<strong>Returns:</strong> An array containing the transformed elements of this
  sequence.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func map&lt;T&gt;(_ transform: (Self.Iterator.Element) throws -&gt; T) rethrows -&gt; [T]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-prefix_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-prefix_">func prefix(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-prefix_"><div class="p">
    <p>Returns a subsequence, up to the specified maximum length, containing
the initial elements of the sequence.</p>

<p>If the maximum length exceeds the number of elements in the sequence,
the result contains all the elements in the sequence.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.prefix(2))
// Prints &quot;[1, 2]&quot;
print(numbers.prefix(10))
// Prints &quot;[1, 2, 3, 4, 5]&quot;</code></pre>

<p><strong><code>maxLength</code>:</strong>  The maximum number of elements to return.
  <code>maxLength</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence starting at the beginning of this sequence
  with at most <code>maxLength</code> elements.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func prefix(_ maxLength: Int) -&gt; Self.SubSequence</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration" id="func-prefix-through_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-prefix-through_">func prefix(<wbr>through:)</a>
        
<div class="comment collapse" id="comment-func-prefix-through_"><div class="p">
    <p>Returns a subsequence from the start of the collection through the
specified position.</p>

<p>The resulting subsequence <em>includes</em> the element at the position <code>end</code>. 
The following example searches for the index of the number <code>40</code> in an
array of integers, and then prints the prefix of the array up to, and
including, that index:</p>

<pre><code class="language-swift">let numbers = [10, 20, 30, 40, 50, 60]
if let i = numbers.index(of: 40) {
    print(numbers.prefix(through: i))
}
// Prints &quot;[10, 20, 30, 40]&quot;</code></pre>

<p><strong><code>end</code>:</strong>  The index of the last element to include in the
  resulting subsequence. <code>end</code> must be a valid index of the collection
  that is not equal to the <code>endIndex</code> property.
<strong>Returns:</strong> A subsequence up to, and including, the <code>end</code> position.</p>

<p><strong>Complexity:</strong> O(1)
<strong>See Also:</strong> <code>prefix(upTo:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func prefix(through position: Self.Index) -&gt; Self.SubSequence</code>
    
    
</div></div>
</div>
<div class="declaration" id="func-prefix-upto_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-prefix-upto_">func prefix(<wbr>upTo:)</a>
        
<div class="comment collapse" id="comment-func-prefix-upto_"><div class="p">
    <p>Returns a subsequence from the start of the collection up to, but not
including, the specified position.</p>

<p>The resulting subsequence <em>does not include</em> the element at the position
<code>end</code>. The following example searches for the index of the number <code>40</code>
in an array of integers, and then prints the prefix of the array up to,
but not including, that index:</p>

<pre><code class="language-swift">let numbers = [10, 20, 30, 40, 50, 60]
if let i = numbers.index(of: 40) {
    print(numbers.prefix(upTo: i))
}
// Prints &quot;[10, 20, 30]&quot;</code></pre>

<p>Passing the collection&#39;s starting index as the <code>end</code> parameter results in
an empty subsequence.</p>

<pre><code class="language-swift">print(numbers.prefix(upTo: numbers.startIndex))
// Prints &quot;[]&quot;</code></pre>

<p><strong><code>end</code>:</strong>  The &quot;past the end&quot; index of the resulting subsequence.
  <code>end</code> must be a valid index of the collection.
<strong>Returns:</strong> A subsequence up to, but not including, the <code>end</code> position.</p>

<p><strong>Complexity:</strong> O(1)
<strong>See Also:</strong> <code>prefix(through:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func prefix(upTo end: Self.Index) -&gt; Self.SubSequence</code>
    
    
</div></div>
</div>
<div class="declaration inherited" id="func-split_omittingemptysubsequences_whereseparator_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-split_omittingemptysubsequences_whereseparator_">func split(<wbr>_:<wbr>omittingEmptySubsequences:<wbr>whereSeparator:)</a>
        
<div class="comment collapse" id="comment-func-split_omittingemptysubsequences_whereseparator_"><div class="p">
    <p>Returns the longest possible subsequences of the sequence, in order, that
don&#39;t contain elements satisfying the given predicate.</p>

<p>The resulting array consists of at most <code>maxSplits + 1</code> subsequences.
Elements that are used to split the sequence are not returned as part of
any subsequence.</p>

<p>The following examples show the effects of the <code>maxSplits</code> and
<code>omittingEmptySubsequences</code> parameters when splitting a string using a
closure that matches spaces. The first use of <code>split</code> returns each word
that was originally separated by one or more spaces.</p>

<pre><code class="language-swift">let line = &quot;BLANCHE:   I don&#39;t want realism. I want magic!&quot;
print(line.characters.split(whereSeparator: { $0 == &quot; &quot; })
                     .map(String.init))
// Prints &quot;[&quot;BLANCHE:&quot;, &quot;I&quot;, &quot;don\&#39;t&quot;, &quot;want&quot;, &quot;realism.&quot;, &quot;I&quot;, &quot;want&quot;, &quot;magic!&quot;]&quot;</code></pre>

<p>The second example passes <code>1</code> for the <code>maxSplits</code> parameter, so the
original string is split just once, into two new strings.</p>

<pre><code class="language-swift">print(
    line.characters.split(maxSplits: 1, whereSeparator: { $0 == &quot; &quot; })
                   .map(String.init))
// Prints &quot;[&quot;BLANCHE:&quot;, &quot;  I don\&#39;t want realism. I want magic!&quot;]&quot;</code></pre>

<p>The final example passes <code>false</code> for the <code>omittingEmptySubsequences</code>
parameter, so the returned array contains empty strings where spaces
were repeated.</p>

<pre><code class="language-swift">print(
    line.characters.split(
        omittingEmptySubsequences: false, 
        whereSeparator: { $0 == &quot; &quot; })
    ).map(String.init))
// Prints &quot;[&quot;BLANCHE:&quot;, &quot;&quot;, &quot;&quot;, &quot;I&quot;, &quot;don\&#39;t&quot;, &quot;want&quot;, &quot;realism.&quot;, &quot;I&quot;, &quot;want&quot;, &quot;magic!&quot;]&quot;</code></pre>

<p><strong>Parameters:</strong>
  <strong>maxSplits:</strong> The maximum number of times to split the sequence, or one
    less than the number of subsequences to return. If <code>maxSplits + 1</code>
    subsequences are returned, the last one is a suffix of the original
    sequence containing the remaining elements. <code>maxSplits</code> must be
    greater than or equal to zero. The default value is <code>Int.max</code>.
  <strong>omittingEmptySubsequences:</strong> If <code>false</code>, an empty subsequence is
    returned in the result for each pair of consecutive elements
    satisfying the <code>isSeparator</code> predicate and for each element at the
    start or end of the sequence satisfying the <code>isSeparator</code> predicate.
    If <code>true</code>, only nonempty subsequences are returned. The default
    value is <code>true</code>.
  <strong>isSeparator:</strong> A closure that returns <code>true</code> if its argument should be
    used to split the sequence; otherwise, <code>false</code>.
<strong>Returns:</strong> An array of subsequences, split from this sequence&#39;s elements.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func split(maxSplits: Int, omittingEmptySubsequences: Bool, whereSeparator isSeparator: (Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; [Self.SubSequence]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-suffix_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-suffix_">func suffix(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-suffix_"><div class="p">
    <p>Returns a subsequence, up to the given maximum length, containing the
final elements of the sequence.</p>

<p>The sequence must be finite. If the maximum length exceeds the number
of elements in the sequence, the result contains all the elements in
the sequence.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.suffix(2))
// Prints &quot;[4, 5]&quot;
print(numbers.suffix(10))
// Prints &quot;[1, 2, 3, 4, 5]&quot;</code></pre>

<p><strong><code>maxLength</code>:</strong>  The maximum number of elements to return. The
  value of <code>maxLength</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence terminating at the end of this sequence with
  at most <code>maxLength</code> elements.</p>

<p><strong>Complexity:</strong> O(<em>n</em>), where <em>n</em> is the length of the sequence.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func suffix(_ maxLength: Int) -&gt; Self.SubSequence</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration" id="func-suffix-from_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-suffix-from_">func suffix(<wbr>from:)</a>
        
<div class="comment collapse" id="comment-func-suffix-from_"><div class="p">
    <p>Returns a subsequence from the specified position to the end of the
collection.</p>

<p>The following example searches for the index of the number <code>40</code> in an
array of integers, and then prints the suffix of the array starting at
that index:</p>

<pre><code class="language-swift">let numbers = [10, 20, 30, 40, 50, 60]
if let i = numbers.index(of: 40) {
    print(numbers.suffix(from: i))
}
// Prints &quot;[40, 50, 60]&quot;</code></pre>

<p>Passing the collection&#39;s <code>endIndex</code> as the <code>start</code> parameter results in
an empty subsequence.</p>

<pre><code class="language-swift">print(numbers.suffix(from: numbers.endIndex))
// Prints &quot;[]&quot;</code></pre>

<p><strong><code>start</code>:</strong>  The index at which to start the resulting subsequence.
  <code>start</code> must be a valid index of the collection.
<strong>Returns:</strong> A subsequence starting at the <code>start</code> position.</p>

<p><strong>Complexity:</strong> O(1)</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func suffix(from start: Self.Index) -&gt; Self.SubSequence</code>
    
    
</div></div>
</div>


<h3>Default Implementations</h3>





<div class="declaration" id="-var-count_-self-indexdistance">
<a class="toggle-link" data-toggle="collapse" href="#comment--var-count_-self-indexdistance">var count: Self.IndexDistance</a><div class="comment collapse" id="comment--var-count_-self-indexdistance"><div class="p">
    <p>The number of elements in the collection.</p>

<p><strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the length
  of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var count: Self.IndexDistance { get }</code>

    </div></div>
</div>
<div class="declaration" id="-var-first_-self-iterator-element">
<a class="toggle-link" data-toggle="collapse" href="#comment--var-first_-self-iterator-element">var first: Self.Iterator.Element?</a><div class="comment collapse" id="comment--var-first_-self-iterator-element"><div class="p">
    <p>The first element of the collection.</p>

<p>If the collection is empty, the value of this property is <code>nil</code>.</p>

<pre><code class="language-swift">let numbers = [10, 20, 30, 40, 50]
if let firstNumber = numbers.first {
    print(firstNumber)
}
// Prints &quot;10&quot;</code></pre>

    <h4>Declaration</h4>    
    <code class="language-swift">var first: Self.Iterator.Element? { get }</code>

    </div></div>
</div>
<div class="declaration" id="-var-isempty_-bool">
<a class="toggle-link" data-toggle="collapse" href="#comment--var-isempty_-bool">var isEmpty: Bool</a><div class="comment collapse" id="comment--var-isempty_-bool"><div class="p">
    <p>A Boolean value indicating whether the collection is empty.</p>

<p>When you need to check whether your collection is empty, use the
<code>isEmpty</code> property instead of checking that the <code>count</code> property is
equal to zero. For collections that don&#39;t conform to
<code>RandomAccessCollection</code>, accessing the <code>count</code> property iterates
through the elements of the collection.</p>

<pre><code class="language-swift">let horseName = &quot;Silver&quot;
if horseName.characters.isEmpty {
    print(&quot;I&#39;ve been through the desert on a horse with no name.&quot;)
} else {
    print(&quot;Hi ho, \(horseName)!&quot;)
}
// Prints &quot;Hi ho, Silver!&quot;)</code></pre>

<p><strong>Complexity:</strong> O(1)</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var isEmpty: Bool { get }</code>

    </div></div>
</div>
<div class="declaration" id="-var-lazy_-lazycollection-self">
<a class="toggle-link" data-toggle="collapse" href="#comment--var-lazy_-lazycollection-self">var lazy: LazyCollection&lt;Self&gt;</a><div class="comment collapse" id="comment--var-lazy_-lazycollection-self"><div class="p">
    <p>A view onto this collection that provides lazy implementations of
normally eager operations, such as <code>map</code> and <code>filter</code>.</p>

<p>Use the <code>lazy</code> property when chaining operations to prevent
intermediate operations from allocating storage, or when you only
need a part of the final collection to avoid unnecessary computation.</p>

<p><strong>See Also:</strong> <code>LazySequenceProtocol</code>, <code>LazyCollectionProtocol</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var lazy: LazyCollection&lt;Self&gt; { get }</code>

    </div></div>
</div>
<div class="declaration" id="-var-underestimatedcount_-int">
<a class="toggle-link" data-toggle="collapse" href="#comment--var-underestimatedcount_-int">var underestimatedCount: Int</a><div class="comment collapse" id="comment--var-underestimatedcount_-int"><div class="p">
    <p>A value less than or equal to the number of elements in the collection.</p>

<p><strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the length
  of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var underestimatedCount: Int { get }</code>

        <h4>Declared In</h4>
            <a href="../../protocol/Collection/"><code>Collection</code></a>
        ,    <a href="../../protocol/Sequence/"><code>Sequence</code></a>
        </div></div>
</div>

<div class="declaration inherited" id="subscript--subscript_-closedrange-self-index">
<a class="toggle-link" data-toggle="collapse" href="#comment-subscript--subscript_-closedrange-self-index">subscript(_: ClosedRange&lt;Self.Index&gt;)</a>
<div class="comment collapse" id="comment-subscript--subscript_-closedrange-self-index"><div class="p">
    <p>Accesses a contiguous subrange of the collection&#39;s elements.</p>

<p>The accessed slice uses the same indices for the same elements as the
original collection. Always use the slice&#39;s <code>startIndex</code> property
instead of assuming that its indices start at a particular value.</p>

<p>This example demonstrates getting a slice of an array of strings, finding
the index of one of the strings in the slice, and then using that index
in the original array.</p>

<pre><code class="language-swift">let streets = [&quot;Adams&quot;, &quot;Bryant&quot;, &quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]
let streetsSlice = streets[2 ..&lt; streets.endIndex]
print(streetsSlice)
// Prints &quot;[&quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]&quot;

let index = streetsSlice.index(of: &quot;Evarts&quot;)    // 4
print(streets[index!])
// Prints &quot;Evarts&quot;</code></pre>

<p><strong><code>bounds</code>:</strong>  A range of the collection&#39;s indices. The bounds of
  the range must be valid indices of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">subscript(bounds: ClosedRange&lt;Self.Index&gt;) -&gt; Self.SubSequence { get }</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>

<div class="declaration inherited" id="func--contains-where_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--contains-where_">func contains(<wbr>where:)</a>
        
<div class="comment collapse" id="comment-func--contains-where_"><div class="p">
    <p>Returns a Boolean value indicating whether the sequence contains an
element that satisfies the given predicate.</p>

<p>You can use the predicate to check for an element of a type that
doesn&#39;t conform to the <code>Equatable</code> protocol, such as the
<code>HTTPResponse</code> enumeration in this example.</p>

<pre><code class="language-swift">enum HTTPResponse {
    case ok
    case error(Int)
}

let lastThreeResponses: [HTTPResponse] = [.ok, .ok, .error(404)]
let hadError = lastThreeResponses.contains { element in
    if case .error = element {
        return true
    } else {
        return false
    }
}
// &#39;hadError&#39; == true</code></pre>

<p>Alternatively, a predicate can be satisfied by a range of <code>Equatable</code>
elements or a general condition. This example shows how you can check an
array for an expense greater than $100.</p>

<pre><code class="language-swift">let expenses = [21.37, 55.21, 9.32, 10.18, 388.77, 11.41]
let hasBigPurchase = expenses.contains { $0 &gt; 100 }
// &#39;hasBigPurchase&#39; == true</code></pre>

<p><strong><code>predicate</code>:</strong>  A closure that takes an element of the sequence
  as its argument and returns a Boolean value that indicates whether
  the passed element represents a match.
<strong>Returns:</strong> <code>true</code> if the sequence contains an element that satisfies
  <code>predicate</code>; otherwise, <code>false</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func contains(where predicate: (Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; Bool</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--distance-from_to_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--distance-from_to_">func distance(<wbr>from:<wbr>to:)</a>
        
<div class="comment collapse" id="comment-func--distance-from_to_"><div class="p">
    <p>Returns the distance between two indices.</p>

<p>Unless the collection conforms to the <code>BidirectionalCollection</code> protocol,
<code>start</code> must be less than or equal to <code>end</code>.</p>

<p><strong>Parameters:</strong>
  <strong>start:</strong> A valid index of the collection.
  <strong>end:</strong> Another valid index of the collection. If <code>end</code> is equal to
    <code>start</code>, the result is zero.
<strong>Returns:</strong> The distance between <code>start</code> and <code>end</code>. The result can be
  negative only if the collection conforms to the
  <code>BidirectionalCollection</code> protocol.</p>

<p><strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the
  resulting distance.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func distance(from start: Self.Index, to end: Self.Index) -&gt; Self.IndexDistance</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--dropfirst">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--dropfirst">func dropFirst()</a>
        
<div class="comment collapse" id="comment-func--dropfirst"><div class="p">
    <p>Returns a subsequence containing all but the first element of the
sequence.</p>

<p>The following example drops the first element from an array of integers.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.dropFirst())
// Prints &quot;[2, 3, 4, 5]&quot;</code></pre>

<p>If the sequence has no elements, the result is an empty subsequence.</p>

<pre><code class="language-swift">let empty: [Int] = []
print(empty.dropFirst())
// Prints &quot;[]&quot;</code></pre>

<p><strong>Returns:</strong> A subsequence starting after the first element of the
  sequence.</p>

<p><strong>Complexity:</strong> O(1)</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func dropFirst() -&gt; Self.SubSequence</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration" id="func--dropfirst_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--dropfirst_">func dropFirst(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func--dropfirst_"><div class="p">
    <p>Returns a subsequence containing all but the given number of initial
elements.</p>

<p>If the number of elements to drop exceeds the number of elements in
the collection, the result is an empty subsequence.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.dropFirst(2))
// Prints &quot;[3, 4, 5]&quot;
print(numbers.dropFirst(10))
// Prints &quot;[]&quot;</code></pre>

<p><strong><code>n</code>:</strong>  The number of elements to drop from the beginning of
  the collection. <code>n</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence starting after the specified number of
  elements.</p>

<p><strong>Complexity:</strong> O(<em>n</em>), where <em>n</em> is the number of elements to drop from
  the beginning of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func dropFirst(_ n: Int) -&gt; Self.SubSequence</code>
    
    
</div></div>
</div>
<div class="declaration inherited" id="func--droplast">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--droplast">func dropLast()</a>
        
<div class="comment collapse" id="comment-func--droplast"><div class="p">
    <p>Returns a subsequence containing all but the last element of the
sequence.</p>

<p>The sequence must be finite. If the sequence has no elements, the result
is an empty subsequence.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.dropLast())
// Prints &quot;[1, 2, 3, 4]&quot;</code></pre>

<p>If the sequence has no elements, the result is an empty subsequence.</p>

<pre><code class="language-swift">let empty: [Int] = []
print(empty.dropLast())
// Prints &quot;[]&quot;</code></pre>

<p><strong>Returns:</strong> A subsequence leaving off the last element of the sequence.</p>

<p><strong>Complexity:</strong> O(<em>n</em>), where <em>n</em> is the length of the sequence.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func dropLast() -&gt; Self.SubSequence</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration" id="func--droplast_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--droplast_">func dropLast(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func--droplast_"><div class="p">
    <p>Returns a subsequence containing all but the specified number of final
elements.</p>

<p>If the number of elements to drop exceeds the number of elements in the
collection, the result is an empty subsequence.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.dropLast(2))
// Prints &quot;[1, 2, 3]&quot;
print(numbers.dropLast(10))
// Prints &quot;[]&quot;</code></pre>

<p><strong><code>n</code>:</strong>  The number of elements to drop off the end of the
  collection. <code>n</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence that leaves off the specified number of elements
  at the end.</p>

<p><strong>Complexity:</strong> O(<em>n</em>), where <em>n</em> is the length of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func dropLast(_ n: Int) -&gt; Self.SubSequence</code>
    
    
</div></div>
</div>
<div class="declaration inherited" id="func--elementsequal_by_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--elementsequal_by_">func elementsEqual(<wbr>_:<wbr>by:)</a>
        
<div class="comment collapse" id="comment-func--elementsequal_by_"><div class="p">
    <p>Returns a Boolean value indicating whether this sequence and another
sequence contain equivalent elements, using the given predicate as the
equivalence test.</p>

<p>At least one of the sequences must be finite.</p>

<p>The predicate must be a <em>equivalence relation</em> over the elements. That
is, for any elements <code>a</code>, <code>b</code>, and <code>c</code>, the following conditions must
hold:</p>

<ul><li><code>areEquivalent(a, a)</code> is always <code>true</code>. (Reflexivity)</li><li><code>areEquivalent(a, b)</code> implies <code>areEquivalent(b, a)</code>. (Symmetry)</li><li>If <code>areEquivalent(a, b)</code> and <code>areEquivalent(b, c)</code> are both <code>true</code>, then
<code>areEquivalent(a, c)</code> is also <code>true</code>. (Transitivity)</li></ul>

<p><strong>Parameters:</strong>
  <strong>other:</strong> A sequence to compare to this sequence.
  <strong>areEquivalent:</strong> A predicate that returns <code>true</code> if its two arguments
    are equivalent; otherwise, <code>false</code>.
<strong>Returns:</strong> <code>true</code> if this sequence and <code>other</code> contain equivalent items,
  using <code>areEquivalent</code> as the equivalence test; otherwise, <code>false.</code></p>

<p><strong>See Also:</strong> <code>elementsEqual(_:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func elementsEqual&lt;OtherSequence where OtherSequence : Sequence, OtherSequence.Iterator.Element == Iterator.Element&gt;(_ other: OtherSequence, by areEquivalent: (Self.Iterator.Element, Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; Bool</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--enumerated">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--enumerated">func enumerated()</a>
        
<div class="comment collapse" id="comment-func--enumerated"><div class="p">
    <p>Returns a sequence of pairs (<em>n</em>, <em>x</em>), where <em>n</em> represents a
consecutive integer starting at zero, and <em>x</em> represents an element of
the sequence.</p>

<p>This example enumerates the characters of the string &quot;Swift&quot; and prints
each character along with its place in the string.</p>

<pre><code class="language-swift">for (n, c) in &quot;Swift&quot;.characters.enumerated() {
    print(&quot;\(n): &#39;\(c)&#39;&quot;)
}
// Prints &quot;0: &#39;S&#39;&quot;
// Prints &quot;1: &#39;w&#39;&quot;
// Prints &quot;2: &#39;i&#39;&quot;
// Prints &quot;3: &#39;f&#39;&quot;
// Prints &quot;4: &#39;t&#39;&quot;</code></pre>

<p>When enumerating a collection, the integer part of each pair is a counter
for the enumeration, not necessarily the index of the paired value.
These counters can only be used as indices in instances of zero-based,
integer-indexed collections, such as <code>Array</code> and <code>ContiguousArray</code>. For
other collections the counters may be out of range or of the wrong type
to use as an index. To iterate over the elements of a collection with its
indices, use the <code>zip(_:_:)</code> function.</p>

<p>This example iterates over the indices and elements of a set, building a
list of indices of names with five or fewer letters.</p>

<pre><code class="language-swift">let names: Set = [&quot;Sofia&quot;, &quot;Camilla&quot;, &quot;Martina&quot;, &quot;Mateo&quot;, &quot;Nicolás&quot;]
var shorterIndices: [SetIndex&lt;String&gt;] = []
for (i, name) in zip(names.indices, names) {
    if name.characters.count &lt;= 5 {
        shorterIndices.append(i)
    }
}</code></pre>

<p>Now that the <code>shorterIndices</code> array holds the indices of the shorter
names in the <code>names</code> set, you can use those indices to access elements in
the set.</p>

<pre><code class="language-swift">for i in shorterIndices {
    print(names[i])
}
// Prints &quot;Sofia&quot;
// Prints &quot;Mateo&quot;</code></pre>

<p><strong>Returns:</strong> A sequence of pairs enumerating the sequence.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func enumerated() -&gt; EnumeratedSequence&lt;Self&gt;</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--filter_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--filter_">func filter(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func--filter_"><div class="p">
    <p>Returns an array containing, in order, the elements of the sequence
that satisfy the given predicate.</p>

<p>In this example, <code>filter</code> is used to include only names shorter than
five characters.</p>

<pre><code class="language-swift">let cast = [&quot;Vivien&quot;, &quot;Marlon&quot;, &quot;Kim&quot;, &quot;Karl&quot;]
let shortNames = cast.filter { $0.characters.count &lt; 5 }
print(shortNames)
// Prints &quot;[&quot;Kim&quot;, &quot;Karl&quot;]&quot;</code></pre>

<p><strong><code>shouldInclude</code>:</strong>  A closure that takes an element of the
  sequence as its argument and returns a Boolean value indicating
  whether the element should be included in the returned array.
<strong>Returns:</strong> An array of the elements that <code>includeElement</code> allowed.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func filter(_ isIncluded: (Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; [Self.Iterator.Element]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--first-where_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--first-where_">func first(<wbr>where:)</a>
        
<div class="comment collapse" id="comment-func--first-where_"><div class="p">
    <p>Returns the first element of the sequence that satisfies the given
predicate or nil if no such element is found.</p>

<p><strong><code>predicate</code>:</strong>  A closure that takes an element of the
  sequence as its argument and returns a Boolean value indicating
  whether the element is a match.
<strong>Returns:</strong> The first match or <code>nil</code> if there was no match.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func first(where predicate: (Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; Self.Iterator.Element?</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--flatmap-elementofresult_-self-iterator-element-throws-elementofresult">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--flatmap-elementofresult_-self-iterator-element-throws-elementofresult">func flatMap&lt;ElementOfResult&gt;(<wbr>_: (Self.Iterator.Element) throws -&gt; ElementOfResult?)</a>
        
<div class="comment collapse" id="comment-func--flatmap-elementofresult_-self-iterator-element-throws-elementofresult"><div class="p">
    <p>Returns an array containing the non-<code>nil</code> results of calling the given
transformation with each element of this sequence.</p>

<p>Use this method to receive an array of nonoptional values when your
transformation produces an optional value.</p>

<p>In this example, note the difference in the result of using <code>map</code> and
<code>flatMap</code> with a transformation that returns an optional <code>Int</code> value.</p>

<pre><code class="language-swift">let possibleNumbers = [&quot;1&quot;, &quot;2&quot;, &quot;three&quot;, &quot;///4///&quot;, &quot;5&quot;]

let mapped: [Int?] = numbers.map { str in Int(str) }
// [1, 2, nil, nil, 5]

let flatMapped: [Int] = numbers.flatMap { str in Int(str) }
// [1, 2, 5]</code></pre>

<p><strong><code>transform</code>:</strong>  A closure that accepts an element of this
  sequence as its argument and returns an optional value.
<strong>Returns:</strong> An array of the non-<code>nil</code> results of calling <code>transform</code>
  with each element of the sequence.</p>

<p><strong>Complexity:</strong> O(<em>m</em> + <em>n</em>), where <em>m</em> is the length of this sequence
  and <em>n</em> is the length of the result.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func flatMap&lt;ElementOfResult&gt;(_ transform: (Self.Iterator.Element) throws -&gt; ElementOfResult?) rethrows -&gt; [ElementOfResult]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--flatmap-segmentofresult_-sequence_-self-iterator-element-throws-segmentofresult">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--flatmap-segmentofresult_-sequence_-self-iterator-element-throws-segmentofresult">func <wbr>flatMap&lt;SegmentOfResult : Sequence&gt;(<wbr>_: (Self.Iterator.Element) throws -&gt; SegmentOfResult)</a>
        
<div class="comment collapse" id="comment-func--flatmap-segmentofresult_-sequence_-self-iterator-element-throws-segmentofresult"><div class="p">
    <p>Returns an array containing the concatenated results of calling the
given transformation with each element of this sequence.</p>

<p>Use this method to receive a single-level collection when your
transformation produces a sequence or collection for each element.</p>

<p>In this example, note the difference in the result of using <code>map</code> and
<code>flatMap</code> with a transformation that returns an array.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4]

let mapped = numbers.map { Array(count: $0, repeatedValue: $0) }
// [[1], [2, 2], [3, 3, 3], [4, 4, 4, 4]]

let flatMapped = numbers.flatMap { Array(count: $0, repeatedValue: $0) }
// [1, 2, 2, 3, 3, 3, 4, 4, 4, 4]</code></pre>

<p>In fact, <code>s.flatMap(transform)</code>  is equivalent to
<code>Array(s.map(transform).joined())</code>.</p>

<p><strong><code>transform</code>:</strong>  A closure that accepts an element of this
  sequence as its argument and returns a sequence or collection.
<strong>Returns:</strong> The resulting flattened array.</p>

<p><strong>Complexity:</strong> O(<em>m</em> + <em>n</em>), where <em>m</em> is the length of this sequence
  and <em>n</em> is the length of the result.
<strong>See Also:</strong> <code>joined()</code>, <code>map(_:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func flatMap&lt;SegmentOfResult : Sequence&gt;(_ transform: (Self.Iterator.Element) throws -&gt; SegmentOfResult) rethrows -&gt; [SegmentOfResult.Iterator.Element]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--foreach_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--foreach_">func forEach(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func--foreach_"><div class="p">
    <p>Calls the given closure on each element in the sequence in the same order
as a <code>for</code>-<code>in</code> loop.</p>

<p>The two loops in the following example produce the same output:</p>

<pre><code class="language-swift">let numberWords = [&quot;one&quot;, &quot;two&quot;, &quot;three&quot;]
for word in numberWords {
    print(word)
}
// Prints &quot;one&quot;
// Prints &quot;two&quot;
// Prints &quot;three&quot;

numberWords.forEach { word in
    print(word)
}
// Same as above</code></pre>

<p>Using the <code>forEach</code> method is distinct from a <code>for</code>-<code>in</code> loop in two
important ways:</p>

<ol><li>You cannot use a <code>break</code> or <code>continue</code> statement to exit the current
call of the <code>body</code> closure or skip subsequent calls.</li><li>Using the <code>return</code> statement in the <code>body</code> closure will exit only from
the current call to <code>body</code>, not from any outer scope, and won&#39;t skip
subsequent calls.</li></ol>

<p><strong><code>body</code>:</strong>  A closure that takes an element of the sequence as a
  parameter.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func forEach(_ body: (Self.Iterator.Element) throws -&gt; Swift.Void) rethrows</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--formindex_offsetby_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--formindex_offsetby_">func formIndex(<wbr>_:<wbr>offsetBy:)</a>
        
<div class="comment collapse" id="comment-func--formindex_offsetby_"><div class="p">
    <p>Offsets the given index by the specified distance.</p>

<p>The value passed as <code>n</code> must not offset <code>i</code> beyond the <code>endIndex</code> or
before the <code>startIndex</code> of this collection.</p>

<p><strong>Parameters:</strong>
  <strong>i:</strong> A valid index of the collection.
  <strong>n:</strong> The distance to offset <code>i</code>. <code>n</code> must not be negative unless the
    collection conforms to the <code>BidirectionalCollection</code> protocol.</p>

<p><strong>See Also:</strong> <code>index(_:offsetBy:)</code>, <code>formIndex(_:offsetBy:limitedBy:)</code>
<strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the absolute
  value of <code>n</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func formIndex(_ i: inout Self.Index, offsetBy n: Self.IndexDistance)</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--formindex_offsetby_limitedby_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--formindex_offsetby_limitedby_">func formIndex(<wbr>_:<wbr>offsetBy:<wbr>limitedBy:)</a>
        
<div class="comment collapse" id="comment-func--formindex_offsetby_limitedby_"><div class="p">
    <p>Offsets the given index by the specified distance, or so that it equals
the given limiting index.</p>

<p>The value passed as <code>n</code> must not offset <code>i</code> beyond the <code>endIndex</code> or
before the <code>startIndex</code> of this collection, unless the index passed as
<code>limit</code> prevents offsetting beyond those bounds.</p>

<p><strong>Parameters:</strong>
  <strong>i:</strong> A valid index of the collection.
  <strong>n:</strong> The distance to offset <code>i</code>. <code>n</code> must not be negative unless the
    collection conforms to the <code>BidirectionalCollection</code> protocol.
<strong>Returns:</strong> <code>true</code> if <code>i</code> has been offset by exactly <code>n</code> steps without
  going beyond <code>limit</code>; otherwise, <code>false</code>. When the return value is
  <code>false</code>, the value of <code>i</code> is equal to <code>limit</code>.</p>

<p><strong>See Also:</strong> <code>index(_:offsetBy:)</code>, <code>formIndex(_:offsetBy:limitedBy:)</code>
<strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the absolute
  value of <code>n</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func formIndex(_ i: inout Self.Index, offsetBy n: Self.IndexDistance, limitedBy limit: Self.Index) -&gt; Bool</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--formindex-after_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--formindex-after_">func formIndex(<wbr>after:)</a>
        
<div class="comment collapse" id="comment-func--formindex-after_"><div class="p">
    <p>Replaces the given index with its successor.</p>

<p><strong><code>i</code>:</strong>  A valid index of the collection. <code>i</code> must be less than
  <code>endIndex</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func formIndex(after i: inout Self.Index)</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--index_offsetby_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--index_offsetby_">func index(<wbr>_:<wbr>offsetBy:)</a>
        
<div class="comment collapse" id="comment-func--index_offsetby_"><div class="p">
    <p>Returns an index that is the specified distance from the given index.</p>

<p>The following example obtains an index advanced four positions from a
string&#39;s starting index and then prints the character at that position.</p>

<pre><code class="language-swift">let s = &quot;Swift&quot;
let i = s.index(s.startIndex, offsetBy: 4)
print(s[i])
// Prints &quot;t&quot;</code></pre>

<p>The value passed as <code>n</code> must not offset <code>i</code> beyond the <code>endIndex</code> or
before the <code>startIndex</code> of this collection.</p>

<p><strong>Parameters:</strong>
  <strong>i:</strong> A valid index of the collection.
  <strong>n:</strong> The distance to offset <code>i</code>. <code>n</code> must not be negative unless the
    collection conforms to the <code>BidirectionalCollection</code> protocol.
<strong>Returns:</strong> An index offset by <code>n</code> from the index <code>i</code>. If <code>n</code> is positive,
  this is the same value as the result of <code>n</code> calls to <code>index(after:)</code>.
  If <code>n</code> is negative, this is the same value as the result of <code>-n</code> calls
  to <code>index(before:)</code>.</p>

<p><strong>See Also:</strong> <code>index(_:offsetBy:limitedBy:)</code>, <code>formIndex(_:offsetBy:)</code>
<strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the absolute
  value of <code>n</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func index(_ i: Self.Index, offsetBy n: Self.IndexDistance) -&gt; Self.Index</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--index_offsetby_limitedby_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--index_offsetby_limitedby_">func index(<wbr>_:<wbr>offsetBy:<wbr>limitedBy:)</a>
        
<div class="comment collapse" id="comment-func--index_offsetby_limitedby_"><div class="p">
    <p>Returns an index that is the specified distance from the given index,
unless that distance is beyond a given limiting index.</p>

<p>The following example obtains an index advanced four positions from a
string&#39;s starting index and then prints the character at that position.
The operation doesn&#39;t require going beyond the limiting <code>s.endIndex</code>
value, so it succeeds.</p>

<pre><code class="language-swift">let s = &quot;Swift&quot;
if let i = s.index(s.startIndex, offsetBy: 4, limitedBy: s.endIndex) {
    print(s[i])
}
// Prints &quot;t&quot;</code></pre>

<p>The next example attempts to retrieve an index six positions from
<code>s.startIndex</code> but fails, because that distance is beyond the index
passed as <code>limit</code>.</p>

<pre><code class="language-swift">let j = s.index(s.startIndex, offsetBy: 6, limitedBy: s.endIndex)
print(j)
// Prints &quot;nil&quot;</code></pre>

<p>The value passed as <code>n</code> must not offset <code>i</code> beyond the <code>endIndex</code> or
before the <code>startIndex</code> of this collection, unless the index passed as
<code>limit</code> prevents offsetting beyond those bounds.</p>

<p><strong>Parameters:</strong>
  <strong>i:</strong> A valid index of the collection.
  <strong>n:</strong> The distance to offset <code>i</code>. <code>n</code> must not be negative unless the
    collection conforms to the <code>BidirectionalCollection</code> protocol.
  <strong>limit:</strong> A valid index of the collection to use as a limit. If <code>n &gt; 0</code>,
    a limit that is less than <code>i</code> has no effect. Likewise, if <code>n &lt; 0</code>, a
    limit that is greater than <code>i</code> has no effect.
<strong>Returns:</strong> An index offset by <code>n</code> from the index <code>i</code>, unless that index
  would be beyond <code>limit</code> in the direction of movement. In that case,
  the method returns <code>nil</code>.</p>

<p><strong>See Also:</strong> <code>index(_:offsetBy:)</code>, <code>formIndex(_:offsetBy:limitedBy:)</code>
<strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>), where <em>n</em> is the absolute
  value of <code>n</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func index(_ i: Self.Index, offsetBy n: Self.IndexDistance, limitedBy limit: Self.Index) -&gt; Self.Index?</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration" id="func--index-where_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--index-where_">func index(<wbr>where:)</a>
        
<div class="comment collapse" id="comment-func--index-where_"><div class="p">
    <p>Returns the first index in which an element of the collection satisfies
the given predicate.</p>

<p>You can use the predicate to find an element of a type that doesn&#39;t
conform to the <code>Equatable</code> protocol or to find an element that matches
particular criteria. Here&#39;s an example that finds a student name that
begins with the letter &quot;A&quot;:</p>

<pre><code class="language-swift">let students = [&quot;Kofi&quot;, &quot;Abena&quot;, &quot;Peter&quot;, &quot;Kweku&quot;, &quot;Akosua&quot;]
if let i = students.index(where: { $0.hasPrefix(&quot;A&quot;) }) {
    print(&quot;\(students[i]) starts with &#39;A&#39;!&quot;)
}
// Prints &quot;Abena starts with &#39;A&#39;!&quot;</code></pre>

<p><strong><code>predicate</code>:</strong>  A closure that takes an element as its argument
  and returns a Boolean value that indicates whether the passed element
  represents a match.
<strong>Returns:</strong> The index of the first element for which <code>predicate</code> returns
  <code>true</code>. If no elements in the collection satisfy the given predicate,
  returns <code>nil</code>.</p>

<p><strong>See Also:</strong> <code>index(of:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func index(where predicate: (Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; Self.Index?</code>
    
    
</div></div>
</div>
<div class="declaration inherited" id="func--lexicographicallyprecedes_by_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--lexicographicallyprecedes_by_">func lexicographicallyPrecedes(<wbr>_:<wbr>by:)</a>
        
<div class="comment collapse" id="comment-func--lexicographicallyprecedes_by_"><div class="p">
    <p>Returns a Boolean value indicating whether the sequence precedes another
sequence in a lexicographical (dictionary) ordering, using the given
predicate to compare elements.</p>

<p>The predicate must be a <em>strict weak ordering</em> over the elements. That
is, for any elements <code>a</code>, <code>b</code>, and <code>c</code>, the following conditions must
hold:</p>

<ul><li><code>areInIncreasingOrder(a, a)</code> is always <code>false</code>. (Irreflexivity)</li><li>If <code>areInIncreasingOrder(a, b)</code> and <code>areInIncreasingOrder(b, c)</code> are
both <code>true</code>, then <code>areInIncreasingOrder(a, c)</code> is also
<code>true</code>. (Transitive comparability)</li><li>Two elements are <em>incomparable</em> if neither is ordered before the other
according to the predicate. If <code>a</code> and <code>b</code> are incomparable, and <code>b</code>
and <code>c</code> are incomparable, then <code>a</code> and <code>c</code> are also incomparable.
(Transitive incomparability)</li></ul>

<p><strong>Parameters:</strong>
  <strong>other:</strong> A sequence to compare to this sequence.
  <strong>areInIncreasingOrder:</strong>  A predicate that returns <code>true</code> if its first
    argument should be ordered before its second argument; otherwise,
    <code>false</code>.
<strong>Returns:</strong> <code>true</code> if this sequence precedes <code>other</code> in a dictionary
  ordering as ordered by <code>areInIncreasingOrder</code>; otherwise, <code>false</code>.</p>

<p><strong>Note:</strong> This method implements the mathematical notion of lexicographical
  ordering, which has no connection to Unicode.  If you are sorting
  strings to present to the end user, use <code>String</code> APIs that perform
  localized comparison instead.
<strong>See Also:</strong> <code>lexicographicallyPrecedes(_:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func lexicographicallyPrecedes&lt;OtherSequence where OtherSequence : Sequence, OtherSequence.Iterator.Element == Iterator.Element&gt;(_ other: OtherSequence, by areInIncreasingOrder: (Self.Iterator.Element, Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; Bool</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration" id="func--map_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--map_">func map(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func--map_"><div class="p">
    <p>Returns an array containing the results of mapping the given closure
over the sequence&#39;s elements.</p>

<p>In this example, <code>map</code> is used first to convert the names in the array
to lowercase strings and then to count their characters.</p>

<pre><code class="language-swift">let cast = [&quot;Vivien&quot;, &quot;Marlon&quot;, &quot;Kim&quot;, &quot;Karl&quot;]
let lowercaseNames = cast.map { $0.lowercaseString }
// &#39;lowercaseNames&#39; == [&quot;vivien&quot;, &quot;marlon&quot;, &quot;kim&quot;, &quot;karl&quot;]
let letterCounts = cast.map { $0.characters.count }
// &#39;letterCounts&#39; == [6, 6, 3, 4]</code></pre>

<p><strong><code>transform</code>:</strong>  A mapping closure. <code>transform</code> accepts an
  element of this sequence as its parameter and returns a transformed
  value of the same or of a different type.
<strong>Returns:</strong> An array containing the transformed elements of this
  sequence.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func map&lt;T&gt;(_ transform: (Self.Iterator.Element) throws -&gt; T) rethrows -&gt; [T]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Collection/"><code>Collection</code></a>,    <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--max-by_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--max-by_">@warn_unqualified_access
     func max(<wbr>by:)</a>
        
<div class="comment collapse" id="comment-func--max-by_"><div class="p">
    <p>Returns the maximum element in the sequence, using the given predicate
as the comparison between elements.</p>

<p>The predicate must be a <em>strict weak ordering</em> over the elements. That
is, for any elements <code>a</code>, <code>b</code>, and <code>c</code>, the following conditions must
hold:</p>

<ul><li><code>areInIncreasingOrder(a, a)</code> is always <code>false</code>. (Irreflexivity)</li><li>If <code>areInIncreasingOrder(a, b)</code> and <code>areInIncreasingOrder(b, c)</code> are
both <code>true</code>, then <code>areInIncreasingOrder(a, c)</code> is also
<code>true</code>. (Transitive comparability)</li><li>Two elements are <em>incomparable</em> if neither is ordered before the other
according to the predicate. If <code>a</code> and <code>b</code> are incomparable, and <code>b</code>
and <code>c</code> are incomparable, then <code>a</code> and <code>c</code> are also incomparable.
(Transitive incomparability)</li></ul>

<p>This example shows how to use the <code>max(by:)</code> method on a
dictionary to find the key-value pair with the highest value.</p>

<pre><code class="language-swift">let hues = [&quot;Heliotrope&quot;: 296, &quot;Coral&quot;: 16, &quot;Aquamarine&quot;: 156]
let greatestHue = hues.max { a, b in a.value &lt; b.value }
print(greatestHue)
// Prints &quot;Optional((&quot;Heliotrope&quot;, 296))&quot;</code></pre>

<p><strong><code>areInIncreasingOrder</code>:</strong>   A predicate that returns <code>true</code> if its
  first argument should be ordered before its second argument;
  otherwise, <code>false</code>.
<strong>Returns:</strong> The sequence&#39;s maximum element if the sequence is not empty;
  otherwise, <code>nil</code>.</p>

<p><strong>See Also:</strong> <code>max()</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">@warn_unqualified_access
     func max(by areInIncreasingOrder: (Self.Iterator.Element, Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; Self.Iterator.Element?</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--min-by_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--min-by_">@warn_unqualified_access
     func min(<wbr>by:)</a>
        
<div class="comment collapse" id="comment-func--min-by_"><div class="p">
    <p>Returns the minimum element in the sequence, using the given predicate as
the comparison between elements.</p>

<p>The predicate must be a <em>strict weak ordering</em> over the elements. That
is, for any elements <code>a</code>, <code>b</code>, and <code>c</code>, the following conditions must
hold:</p>

<ul><li><code>areInIncreasingOrder(a, a)</code> is always <code>false</code>. (Irreflexivity)</li><li>If <code>areInIncreasingOrder(a, b)</code> and <code>areInIncreasingOrder(b, c)</code> are
both <code>true</code>, then <code>areInIncreasingOrder(a, c)</code> is also
<code>true</code>. (Transitive comparability)</li><li>Two elements are <em>incomparable</em> if neither is ordered before the other
according to the predicate. If <code>a</code> and <code>b</code> are incomparable, and <code>b</code>
and <code>c</code> are incomparable, then <code>a</code> and <code>c</code> are also incomparable.
(Transitive incomparability)</li></ul>

<p>This example shows how to use the <code>min(by:)</code> method on a
dictionary to find the key-value pair with the lowest value.</p>

<pre><code class="language-swift">let hues = [&quot;Heliotrope&quot;: 296, &quot;Coral&quot;: 16, &quot;Aquamarine&quot;: 156]
let leastHue = hues.min { a, b in a.value &lt; b.value }
print(leastHue)
// Prints &quot;Optional((&quot;Coral&quot;, 16))&quot;</code></pre>

<p><strong><code>areInIncreasingOrder</code>:</strong>  A predicate that returns <code>true</code>
  if its first argument should be ordered before its second
  argument; otherwise, <code>false</code>.
<strong>Returns:</strong> The sequence&#39;s minimum element, according to
  <code>areInIncreasingOrder</code>. If the sequence has no elements, returns
  <code>nil</code>.</p>

<p><strong>See Also:</strong> <code>min()</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">@warn_unqualified_access
     func min(by areInIncreasingOrder: (Self.Iterator.Element, Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; Self.Iterator.Element?</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration" id="func--prefix_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--prefix_">func prefix(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func--prefix_"><div class="p">
    <p>Returns a subsequence, up to the specified maximum length, containing
the initial elements of the collection.</p>

<p>If the maximum length exceeds the number of elements in the collection,
the result contains all the elements in the collection.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.prefix(2))
// Prints &quot;[1, 2]&quot;
print(numbers.prefix(10))
// Prints &quot;[1, 2, 3, 4, 5]&quot;</code></pre>

<p><strong><code>maxLength</code>:</strong>  The maximum number of elements to return.
  <code>maxLength</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence starting at the beginning of this collection
  with at most <code>maxLength</code> elements.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func prefix(_ maxLength: Int) -&gt; Self.SubSequence</code>
    
    
</div></div>
</div>
<div class="declaration" id="func--prefix-through_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--prefix-through_">func prefix(<wbr>through:)</a>
        
<div class="comment collapse" id="comment-func--prefix-through_"><div class="p">
    <p>Returns a subsequence from the start of the collection through the
specified position.</p>

<p>The resulting subsequence <em>includes</em> the element at the position <code>end</code>. 
The following example searches for the index of the number <code>40</code> in an
array of integers, and then prints the prefix of the array up to, and
including, that index:</p>

<pre><code class="language-swift">let numbers = [10, 20, 30, 40, 50, 60]
if let i = numbers.index(of: 40) {
    print(numbers.prefix(through: i))
}
// Prints &quot;[10, 20, 30, 40]&quot;</code></pre>

<p><strong><code>end</code>:</strong>  The index of the last element to include in the
  resulting subsequence. <code>end</code> must be a valid index of the collection
  that is not equal to the <code>endIndex</code> property.
<strong>Returns:</strong> A subsequence up to, and including, the <code>end</code> position.</p>

<p><strong>Complexity:</strong> O(1)
<strong>See Also:</strong> <code>prefix(upTo:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func prefix(through position: Self.Index) -&gt; Self.SubSequence</code>
    
    
</div></div>
</div>
<div class="declaration" id="func--prefix-upto_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--prefix-upto_">func prefix(<wbr>upTo:)</a>
        
<div class="comment collapse" id="comment-func--prefix-upto_"><div class="p">
    <p>Returns a subsequence from the start of the collection up to, but not
including, the specified position.</p>

<p>The resulting subsequence <em>does not include</em> the element at the position
<code>end</code>. The following example searches for the index of the number <code>40</code>
in an array of integers, and then prints the prefix of the array up to,
but not including, that index:</p>

<pre><code class="language-swift">let numbers = [10, 20, 30, 40, 50, 60]
if let i = numbers.index(of: 40) {
    print(numbers.prefix(upTo: i))
}
// Prints &quot;[10, 20, 30]&quot;</code></pre>

<p>Passing the collection&#39;s starting index as the <code>end</code> parameter results in
an empty subsequence.</p>

<pre><code class="language-swift">print(numbers.prefix(upTo: numbers.startIndex))
// Prints &quot;[]&quot;</code></pre>

<p><strong><code>end</code>:</strong>  The &quot;past the end&quot; index of the resulting subsequence.
  <code>end</code> must be a valid index of the collection.
<strong>Returns:</strong> A subsequence up to, but not including, the <code>end</code> position.</p>

<p><strong>Complexity:</strong> O(1)
<strong>See Also:</strong> <code>prefix(through:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func prefix(upTo end: Self.Index) -&gt; Self.SubSequence</code>
    
    
</div></div>
</div>
<div class="declaration inherited" id="func--reduce__">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--reduce__">func reduce(<wbr>_:<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func--reduce__"><div class="p">
    <p>Returns the result of calling the given combining closure with each
element of this sequence and an accumulating value.</p>

<p>The <code>nextPartialResult</code> closure is called sequentially with an
accumulating value initialized to <code>initialResult</code> and each
element of the sequence. This example shows how to find the sum
of an array of numbers.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4]
let addTwo: (Int, Int) -&gt; Int = { x, y in x + y }
let numberSum = numbers.reduce(0, addTwo)
// &#39;numberSum&#39; == 10</code></pre>

<p>When <code>numbers.reduce(_:_:)</code> is called, the
following steps occur:</p>

<ol><li>The <code>nextPartialResult</code> closure is called with the initial
result and the first element of <code>numbers</code>, returning the sum:
<code>1</code>.</li><li>The closure is called again repeatedly with the previous call&#39;s
return value and each element of the sequence.</li><li>When the sequence is exhausted, the last value returned from the
closure is returned to the caller.</li></ol>

<p><strong>Parameters:</strong>
  <strong>initialResult:</strong> the initial accumulating value.
  <strong>nextPartialResult:</strong> A closure that combines an accumulating
    value and an element of the sequence into a new accumulating
    value, to be used in the next call of the
    <code>nextPartialResult</code> closure or returned to the caller.
<strong>Returns:</strong> The final accumulated value.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func reduce&lt;Result&gt;(_ initialResult: Result, _ nextPartialResult: (Result, Self.Iterator.Element) throws -&gt; Result) rethrows -&gt; Result</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--reversed">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--reversed">func reversed()</a>
        
<div class="comment collapse" id="comment-func--reversed"><div class="p">
    <p>Returns an array containing the elements of this sequence in reverse
order.</p>

<p>The sequence must be finite.</p>

<p><strong>Complexity:</strong> O(<em>n</em>), where <em>n</em> is the length of the sequence.</p>

<p><strong>Returns:</strong> An array containing the elements of this sequence in
  reverse order.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func reversed() -&gt; [Self.Iterator.Element]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--sorted-by_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--sorted-by_">func sorted(<wbr>by:)</a>
        
<div class="comment collapse" id="comment-func--sorted-by_"><div class="p">
    <p>Returns the elements of the sequence, sorted using the given
predicate as the comparison between elements.</p>

<p>When you want to sort a sequence of elements that don&#39;t conform to
the <code>Comparable</code> protocol, pass a predicate to this method that returns
<code>true</code> when the first element passed should be ordered before the
second. The elements of the resulting array are ordered according to the
given predicate.</p>

<p>The predicate must be a <em>strict weak ordering</em> over the elements. That
is, for any elements <code>a</code>, <code>b</code>, and <code>c</code>, the following conditions must
hold:</p>

<ul><li><code>areInIncreasingOrder(a, a)</code> is always <code>false</code>. (Irreflexivity)</li><li>If <code>areInIncreasingOrder(a, b)</code> and <code>areInIncreasingOrder(b, c)</code> are
both <code>true</code>, then <code>areInIncreasingOrder(a, c)</code> is also <code>true</code>.
(Transitive comparability)</li><li>Two elements are <em>incomparable</em> if neither is ordered before the other
according to the predicate. If <code>a</code> and <code>b</code> are incomparable, and <code>b</code>
and <code>c</code> are incomparable, then <code>a</code> and <code>c</code> are also incomparable.
(Transitive incomparability)</li></ul>

<p>The sorting algorithm is not stable. A nonstable sort may change the
relative order of elements for which <code>areInIncreasingOrder</code> does not
establish an order.</p>

<p>In the following example, the predicate provides an ordering for an array
of a custom <code>HTTPResponse</code> type. The predicate orders errors before
successes and sorts the error responses by their error code.</p>

<pre><code class="language-swift">enum HTTPResponse {
    case ok
    case error(Int)
}

let responses: [HTTPResponse] = [.error(500), .ok, .ok, .error(404), .error(403)]
let sortedResponses = responses.sorted {
    switch ($0, $1) {
    // Order errors by code
    case let (.error(aCode), .error(bCode)):
        return aCode &lt; bCode

    // All successes are equivalent, so none is before any other
    case (.ok, .ok): return false

    // Order errors before successes
    case (.error, .ok): return true
    case (.ok, .error): return false
    }
}
print(sortedResponses)
// Prints &quot;[.error(403), .error(404), .error(500), .ok, .ok]&quot;</code></pre>

<p>You also use this method to sort elements that conform to the
<code>Comparable</code> protocol in descending order. To sort your sequence
in descending order, pass the greater-than operator (<code>&gt;</code>) as the
<code>areInIncreasingOrder</code> parameter.</p>

<pre><code class="language-swift">let students: Set = [&quot;Kofi&quot;, &quot;Abena&quot;, &quot;Peter&quot;, &quot;Kweku&quot;, &quot;Akosua&quot;]
let descendingStudents = students.sorted(by: &gt;)
print(descendingStudents)
// Prints &quot;[&quot;Peter&quot;, &quot;Kweku&quot;, &quot;Kofi&quot;, &quot;Akosua&quot;, &quot;Abena&quot;]&quot;</code></pre>

<p>Calling the related <code>sorted()</code> method is equivalent to calling this
method and passing the less-than operator (<code>&lt;</code>) as the predicate.</p>

<pre><code class="language-swift">print(students.sorted())
// Prints &quot;[&quot;Abena&quot;, &quot;Akosua&quot;, &quot;Kofi&quot;, &quot;Kweku&quot;, &quot;Peter&quot;]&quot;
print(students.sorted(by: &lt;))
// Prints &quot;[&quot;Abena&quot;, &quot;Akosua&quot;, &quot;Kofi&quot;, &quot;Kweku&quot;, &quot;Peter&quot;]&quot;</code></pre>

<p><strong><code>areInIncreasingOrder</code>:</strong>  A predicate that returns <code>true</code> if its first
  argument should be ordered before its second argument; otherwise,
  <code>false</code>.
<strong>Returns:</strong> A sorted array of the sequence&#39;s elements.</p>

<p><strong>See Also:</strong> <code>sorted()</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func sorted(by areInIncreasingOrder: (Self.Iterator.Element, Self.Iterator.Element) -&gt; Bool) -&gt; [Self.Iterator.Element]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration" id="func--split_omittingemptysubsequences_whereseparator_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--split_omittingemptysubsequences_whereseparator_">func split(<wbr>_:<wbr>omittingEmptySubsequences:<wbr>whereSeparator:)</a>
        
<div class="comment collapse" id="comment-func--split_omittingemptysubsequences_whereseparator_"><div class="p">
    <p>Returns the longest possible subsequences of the collection, in order,
that don&#39;t contain elements satisfying the given predicate.</p>

<p>The resulting array consists of at most <code>maxSplits + 1</code> subsequences.
Elements that are used to split the sequence are not returned as part of
any subsequence.</p>

<p>The following examples show the effects of the <code>maxSplits</code> and
<code>omittingEmptySubsequences</code> parameters when splitting a string using a
closure that matches spaces. The first use of <code>split</code> returns each word
that was originally separated by one or more spaces.</p>

<pre><code class="language-swift">let line = &quot;BLANCHE:   I don&#39;t want realism. I want magic!&quot;
print(line.characters.split(whereSeparator: { $0 == &quot; &quot; })
                     .map(String.init))
// Prints &quot;[&quot;BLANCHE:&quot;, &quot;I&quot;, &quot;don\&#39;t&quot;, &quot;want&quot;, &quot;realism.&quot;, &quot;I&quot;, &quot;want&quot;, &quot;magic!&quot;]&quot;</code></pre>

<p>The second example passes <code>1</code> for the <code>maxSplits</code> parameter, so the
original string is split just once, into two new strings.</p>

<pre><code class="language-swift">print(
    line.characters.split(
        maxSplits: 1, whereSeparator: { $0 == &quot; &quot; }
        ).map(String.init))
// Prints &quot;[&quot;BLANCHE:&quot;, &quot;  I don\&#39;t want realism. I want magic!&quot;]&quot;</code></pre>

<p>The final example passes <code>false</code> for the <code>omittingEmptySubsequences</code>
parameter, so the returned array contains empty strings where spaces
were repeated.</p>

<pre><code class="language-swift">print(line.characters.split(omittingEmptySubsequences: false, whereSeparator: { $0 == &quot; &quot; })
                      .map(String.init))
// Prints &quot;[&quot;BLANCHE:&quot;, &quot;&quot;, &quot;&quot;, &quot;I&quot;, &quot;don\&#39;t&quot;, &quot;want&quot;, &quot;realism.&quot;, &quot;I&quot;, &quot;want&quot;, &quot;magic!&quot;]&quot;</code></pre>

<p><strong>Parameters:</strong>
  <strong>maxSplits:</strong> The maximum number of times to split the collection, or
    one less than the number of subsequences to return. If
    <code>maxSplits + 1</code> subsequences are returned, the last one is a suffix
    of the original collection containing the remaining elements.
    <code>maxSplits</code> must be greater than or equal to zero. The default value
    is <code>Int.max</code>.
  <strong>omittingEmptySubsequences:</strong> If <code>false</code>, an empty subsequence is
    returned in the result for each pair of consecutive elements
    satisfying the <code>isSeparator</code> predicate and for each element at the
    start or end of the collection satisfying the <code>isSeparator</code>
    predicate. The default value is <code>true</code>.
  <strong>isSeparator:</strong> A closure that takes an element as an argument and
    returns a Boolean value indicating whether the collection should be
    split at that element.
<strong>Returns:</strong> An array of subsequences, split from this collection&#39;s
  elements.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func split(maxSplits: Int = default, omittingEmptySubsequences: Bool = default, whereSeparator isSeparator: (Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; [Self.SubSequence]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Collection/"><code>Collection</code></a>,    <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func--starts-with_by_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--starts-with_by_">func starts(<wbr>with:<wbr>by:)</a>
        
<div class="comment collapse" id="comment-func--starts-with_by_"><div class="p">
    <p>Returns a Boolean value indicating whether the initial elements of the
sequence are equivalent to the elements in another sequence, using
the given predicate as the equivalence test.</p>

<p>The predicate must be a <em>equivalence relation</em> over the elements. That
is, for any elements <code>a</code>, <code>b</code>, and <code>c</code>, the following conditions must
hold:</p>

<ul><li><code>areEquivalent(a, a)</code> is always <code>true</code>. (Reflexivity)</li><li><code>areEquivalent(a, b)</code> implies <code>areEquivalent(b, a)</code>. (Symmetry)</li><li>If <code>areEquivalent(a, b)</code> and <code>areEquivalent(b, c)</code> are both <code>true</code>, then
<code>areEquivalent(a, c)</code> is also <code>true</code>. (Transitivity)</li></ul>

<p><strong>Parameters:</strong>
  <strong>possiblePrefix:</strong> A sequence to compare to this sequence.
  <strong>areEquivalent:</strong> A predicate that returns <code>true</code> if its two arguments
    are equivalent; otherwise, <code>false</code>.
<strong>Returns:</strong> <code>true</code> if the initial elements of the sequence are equivalent
  to the elements of <code>possiblePrefix</code>; otherwise, <code>false</code>. If
  <code>possiblePrefix</code> has no elements, the return value is <code>true</code>.</p>

<p><strong>See Also:</strong> <code>starts(with:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func starts&lt;PossiblePrefix where PossiblePrefix : Sequence, PossiblePrefix.Iterator.Element == Iterator.Element&gt;(with possiblePrefix: PossiblePrefix, by areEquivalent: (Self.Iterator.Element, Self.Iterator.Element) throws -&gt; Bool) rethrows -&gt; Bool</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration" id="func--suffix_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--suffix_">func suffix(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func--suffix_"><div class="p">
    <p>Returns a subsequence, up to the given maximum length, containing the
final elements of the collection.</p>

<p>If the maximum length exceeds the number of elements in the collection,
the result contains all the elements in the collection.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.suffix(2))
// Prints &quot;[4, 5]&quot;
print(numbers.suffix(10))
// Prints &quot;[1, 2, 3, 4, 5]&quot;</code></pre>

<p><strong><code>maxLength</code>:</strong>  The maximum number of elements to return. The
  value of <code>maxLength</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence terminating at the end of the collection with at
  most <code>maxLength</code> elements.</p>

<p><strong>Complexity:</strong> O(<em>n</em>), where <em>n</em> is the length of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func suffix(_ maxLength: Int) -&gt; Self.SubSequence</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Collection/"><code>Collection</code></a>,    <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration" id="func--suffix-from_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func--suffix-from_">func suffix(<wbr>from:)</a>
        
<div class="comment collapse" id="comment-func--suffix-from_"><div class="p">
    <p>Returns a subsequence from the specified position to the end of the
collection.</p>

<p>The following example searches for the index of the number <code>40</code> in an
array of integers, and then prints the suffix of the array starting at
that index:</p>

<pre><code class="language-swift">let numbers = [10, 20, 30, 40, 50, 60]
if let i = numbers.index(of: 40) {
    print(numbers.suffix(from: i))
}
// Prints &quot;[40, 50, 60]&quot;</code></pre>

<p>Passing the collection&#39;s <code>endIndex</code> as the <code>start</code> parameter results in
an empty subsequence.</p>

<pre><code class="language-swift">print(numbers.suffix(from: numbers.endIndex))
// Prints &quot;[]&quot;</code></pre>

<p><strong><code>start</code>:</strong>  The index at which to start the resulting subsequence.
  <code>start</code> must be a valid index of the collection.
<strong>Returns:</strong> A subsequence starting at the <code>start</code> position.</p>

<p><strong>Complexity:</strong> O(1)</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func suffix(from start: Self.Index) -&gt; Self.SubSequence</code>
    
    
</div></div>
</div>







<h4>Where Index : Strideable, Index.Stride : SignedInteger</h4>



<div class="declaration inherited" id="subscript-index_-strideable-index-stride_-signedinteger-subscript_-countableclosedrange-self-index">
<a class="toggle-link" data-toggle="collapse" href="#comment-subscript-index_-strideable-index-stride_-signedinteger-subscript_-countableclosedrange-self-index">subscript(_: CountableClosedRange&lt;Self.Index&gt;)</a>
<div class="comment collapse" id="comment-subscript-index_-strideable-index-stride_-signedinteger-subscript_-countableclosedrange-self-index"><div class="p">
    <p>Accesses a contiguous subrange of the collection&#39;s elements.</p>

<p>The accessed slice uses the same indices for the same elements as the
original collection. Always use the slice&#39;s <code>startIndex</code> property
instead of assuming that its indices start at a particular value.</p>

<p>This example demonstrates getting a slice of an array of strings, finding
the index of one of the strings in the slice, and then using that index
in the original array.</p>

<pre><code class="language-swift">let streets = [&quot;Adams&quot;, &quot;Bryant&quot;, &quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]
let streetsSlice = streets[2 ..&lt; streets.endIndex]
print(streetsSlice)
// Prints &quot;[&quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]&quot;

let index = streetsSlice.index(of: &quot;Evarts&quot;)    // 4
print(streets[index!])
// Prints &quot;Evarts&quot;</code></pre>

<p><strong><code>bounds</code>:</strong>  A range of the collection&#39;s indices. The bounds of
  the range must be valid indices of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">subscript(bounds: CountableClosedRange&lt;Self.Index&gt;) -&gt; Self.SubSequence { get }</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="subscript-index_-strideable-index-stride_-signedinteger-subscript_-countablerange-self-index">
<a class="toggle-link" data-toggle="collapse" href="#comment-subscript-index_-strideable-index-stride_-signedinteger-subscript_-countablerange-self-index">subscript(_: CountableRange&lt;Self.Index&gt;)</a>
<div class="comment collapse" id="comment-subscript-index_-strideable-index-stride_-signedinteger-subscript_-countablerange-self-index"><div class="p">
    <p>Accesses a contiguous subrange of the collection&#39;s elements.</p>

<p>The accessed slice uses the same indices for the same elements as the
original collection. Always use the slice&#39;s <code>startIndex</code> property
instead of assuming that its indices start at a particular value.</p>

<p>This example demonstrates getting a slice of an array of strings, finding
the index of one of the strings in the slice, and then using that index
in the original array.</p>

<pre><code class="language-swift">let streets = [&quot;Adams&quot;, &quot;Bryant&quot;, &quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]
let streetsSlice = streets[2 ..&lt; streets.endIndex]
print(streetsSlice)
// Prints &quot;[&quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]&quot;

let index = streetsSlice.index(of: &quot;Evarts&quot;)    // 4
print(streets[index!])
// Prints &quot;Evarts&quot;</code></pre>

<p><strong><code>bounds</code>:</strong>  A range of the collection&#39;s indices. The bounds of
  the range must be valid indices of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">subscript(bounds: CountableRange&lt;Self.Index&gt;) -&gt; Self.SubSequence { get }</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Indexable/"><code>Indexable</code></a>    
</div></div>
</div>






<h4>Where Indices == DefaultIndices<Self></h4>


<div class="declaration" id="indices-defaultindices-self-var-indices_-defaultindices-self">
<a class="toggle-link" data-toggle="collapse" href="#comment-indices-defaultindices-self-var-indices_-defaultindices-self">var indices: DefaultIndices&lt;Self&gt;</a><div class="comment collapse" id="comment-indices-defaultindices-self-var-indices_-defaultindices-self"><div class="p">
    <p>The indices that are valid for subscripting the collection, in ascending
order.</p>

<p>A collection&#39;s <code>indices</code> property can hold a strong reference to the
collection itself, causing the collection to be non-uniquely referenced.
If you mutate the collection while iterating over its indices, a strong
reference can cause an unexpected copy of the collection. To avoid the
unexpected copy, use the <code>index(after:)</code> method starting with
<code>startIndex</code> to produce indices instead.</p>

<pre><code class="language-swift">var c = MyFancyCollection([10, 20, 30, 40, 50])
var i = c.startIndex
while i != c.endIndex {
    c[i] /= 5
    i = c.index(after: i)
}
// c == MyFancyCollection([2, 4, 6, 8, 10])</code></pre>

    <h4>Declaration</h4>    
    <code class="language-swift">var indices: DefaultIndices&lt;Self&gt; { get }</code>

    </div></div>
</div>







<h4>Where Iterator == IndexingIterator<Self></h4>




<div class="declaration" id="func-iterator-indexingiterator-self-makeiterator">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-indexingiterator-self-makeiterator">func makeIterator()</a>
        
<div class="comment collapse" id="comment-func-iterator-indexingiterator-self-makeiterator"><div class="p">
    <p>Returns an iterator over the elements of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func makeIterator() -&gt; IndexingIterator&lt;Self&gt;</code>
    
    
</div></div>
</div>





<h4>Where Iterator == Self, Self : IteratorProtocol</h4>




<div class="declaration inherited" id="func-iterator-self-self_-iteratorprotocol-makeiterator">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-self-self_-iteratorprotocol-makeiterator">func makeIterator()</a>
        
<div class="comment collapse" id="comment-func-iterator-self-self_-iteratorprotocol-makeiterator"><div class="p">
    <p>Returns an iterator over the elements of this sequence.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func makeIterator() -&gt; Self</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>





<h4>Where Iterator.Element : Collection</h4>




<div class="declaration" id="func-iterator-element_-collection-joined">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-collection-joined">func joined()</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-collection-joined"><div class="p">
    <p>Returns the elements of this collection of collections, concatenated.</p>

<p>In this example, an array of three ranges is flattened so that the
elements of each range can be iterated in turn.</p>

<pre><code class="language-swift">let ranges = [0..&lt;3, 8..&lt;10, 15..&lt;17]

// A for-in loop over &#39;ranges&#39; accesses each range:
for range in ranges {
  print(range)
}
// Prints &quot;0..&lt;3&quot;
// Prints &quot;8..&lt;10&quot;
// Prints &quot;15..&lt;17&quot;

// Use &#39;joined()&#39; to access each element of each range:
for index in ranges.joined() {
    print(index, terminator: &quot; &quot;)
}
// Prints: &quot;0 1 2 8 9 15 16&quot;</code></pre>

<p><strong>Returns:</strong> A flattened view of the elements of this
  collection of collections.</p>

<p><strong>See Also:</strong> <code>flatMap(_:)</code>, <code>joined(separator:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func joined() -&gt; FlattenCollection&lt;Self&gt;</code>
    
    
</div></div>
</div>





<h4>Where Iterator.Element : Comparable</h4>




<div class="declaration inherited" id="func-iterator-element_-comparable-lexicographicallyprecedes_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-comparable-lexicographicallyprecedes_">func lexicographicallyPrecedes(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-comparable-lexicographicallyprecedes_"><div class="p">
    <p>Returns a Boolean value indicating whether the sequence precedes another
sequence in a lexicographical (dictionary) ordering, using the
less-than operator (<code>&lt;</code>) to compare elements.</p>

<p>This example uses the <code>lexicographicallyPrecedes</code> method to test which
array of integers comes first in a lexicographical ordering.</p>

<pre><code class="language-swift">let a = [1, 2, 2, 2]
let b = [1, 2, 3, 4]

print(a.lexicographicallyPrecedes(b))
// Prints &quot;true&quot;
print(b.lexicographicallyPrecedes(b))
// Prints &quot;false&quot;</code></pre>

<p><strong><code>other</code>:</strong>  A sequence to compare to this sequence.
<strong>Returns:</strong> <code>true</code> if this sequence precedes <code>other</code> in a dictionary
  ordering; otherwise, <code>false</code>.</p>

<p><strong>Note:</strong> This method implements the mathematical notion of lexicographical
  ordering, which has no connection to Unicode.  If you are sorting
  strings to present to the end user, use <code>String</code> APIs that
  perform localized comparison.
<strong>See Also:</strong> <code>lexicographicallyPrecedes(_:by:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func lexicographicallyPrecedes&lt;OtherSequence where OtherSequence : Sequence, OtherSequence.Iterator.Element == Iterator.Element&gt;(_ other: OtherSequence) -&gt; Bool</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-iterator-element_-comparable-max">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-comparable-max">@warn_unqualified_access
     func max()</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-comparable-max"><div class="p">
    <p>Returns the maximum element in the sequence.</p>

<p>This example finds the smallest value in an array of height measurements.</p>

<pre><code class="language-swift">let heights = [67.5, 65.7, 64.3, 61.1, 58.5, 60.3, 64.9]
let greatestHeight = heights.max()
print(greatestHeight)
// Prints &quot;Optional(67.5)&quot;</code></pre>

<p><strong>Returns:</strong> The sequence&#39;s maximum element. If the sequence has no
  elements, returns <code>nil</code>.</p>

<p><strong>See Also:</strong> <code>max(by:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">@warn_unqualified_access
     func max() -&gt; Self.Iterator.Element?</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-iterator-element_-comparable-min">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-comparable-min">@warn_unqualified_access
     func min()</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-comparable-min"><div class="p">
    <p>Returns the minimum element in the sequence.</p>

<p>This example finds the smallest value in an array of height measurements.</p>

<pre><code class="language-swift">let heights = [67.5, 65.7, 64.3, 61.1, 58.5, 60.3, 64.9]
let lowestHeight = heights.min()
print(lowestHeight)
// Prints &quot;Optional(58.5)&quot;</code></pre>

<p><strong>Returns:</strong> The sequence&#39;s minimum element. If the sequence has no
  elements, returns <code>nil</code>.</p>

<p><strong>See Also:</strong> <code>min(by:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">@warn_unqualified_access
     func min() -&gt; Self.Iterator.Element?</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-iterator-element_-comparable-sorted">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-comparable-sorted">func sorted()</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-comparable-sorted"><div class="p">
    <p>Returns the elements of the sequence, sorted.</p>

<p>You can sort any sequence of elements that conform to the
<code>Comparable</code> protocol by calling this method. Elements are sorted in
ascending order.</p>

<p>The sorting algorithm is not stable. A nonstable sort may change the
relative order of elements that compare equal.</p>

<p>Here&#39;s an example of sorting a list of students&#39; names. Strings in Swift
conform to the <code>Comparable</code> protocol, so the names are sorted in
ascending order according to the less-than operator (<code>&lt;</code>).</p>

<pre><code class="language-swift">let students: Set = [&quot;Kofi&quot;, &quot;Abena&quot;, &quot;Peter&quot;, &quot;Kweku&quot;, &quot;Akosua&quot;]
let sortedStudents = students.sorted()
print(sortedStudents)
// Prints &quot;[&quot;Abena&quot;, &quot;Akosua&quot;, &quot;Kofi&quot;, &quot;Kweku&quot;, &quot;Peter&quot;]&quot;</code></pre>

<p>To sort the elements of your sequence in descending order, pass the
greater-than operator (<code>&gt;</code>) to the <code>sorted(by:)</code> method.</p>

<pre><code class="language-swift">let descendingStudents = students.sorted(by: &gt;)
print(descendingStudents)
// Prints &quot;[&quot;Peter&quot;, &quot;Kweku&quot;, &quot;Kofi&quot;, &quot;Akosua&quot;, &quot;Abena&quot;]&quot;</code></pre>

<p><strong>Returns:</strong> A sorted array of the sequence&#39;s elements.</p>

<p><strong>See Also:</strong> <code>sorted(by:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func sorted() -&gt; [Self.Iterator.Element]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>





<h4>Where Iterator.Element : Equatable</h4>




<div class="declaration inherited" id="func-iterator-element_-equatable-contains_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-equatable-contains_">func contains(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-equatable-contains_"><div class="p">
    <p>Returns a Boolean value indicating whether the sequence contains the
given element.</p>

<p>This example checks to see whether a favorite actor is in an array
storing a movie&#39;s cast.</p>

<pre><code class="language-swift">let cast = [&quot;Vivien&quot;, &quot;Marlon&quot;, &quot;Kim&quot;, &quot;Karl&quot;]
print(cast.contains(&quot;Marlon&quot;))
// Prints &quot;true&quot;
print(cast.contains(&quot;James&quot;))
// Prints &quot;false&quot;</code></pre>

<p><strong><code>element</code>:</strong>  The element to find in the sequence.
<strong>Returns:</strong> <code>true</code> if the element was found in the sequence; otherwise,
  <code>false</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func contains(_ element: Self.Iterator.Element) -&gt; Bool</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-iterator-element_-equatable-elementsequal_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-equatable-elementsequal_">func elementsEqual(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-equatable-elementsequal_"><div class="p">
    <p>Returns a Boolean value indicating whether this sequence and another
sequence contain the same elements in the same order.</p>

<p>At least one of the sequences must be finite.</p>

<p>This example tests whether one countable range shares the same elements
as another countable range and an array.</p>

<pre><code class="language-swift">let a = 1...3
let b = 1...10

print(a.elementsEqual(b))
// Prints &quot;false&quot;
print(a.elementsEqual([1, 2, 3]))
// Prints &quot;true&quot;</code></pre>

<p><strong><code>other</code>:</strong>  A sequence to compare to this sequence.
<strong>Returns:</strong> <code>true</code> if this sequence and <code>other</code> contain the same elements
  in the same order.</p>

<p><strong>See Also:</strong> <code>elementsEqual(_:by:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func elementsEqual&lt;OtherSequence where OtherSequence : Sequence, OtherSequence.Iterator.Element == Iterator.Element&gt;(_ other: OtherSequence) -&gt; Bool</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration" id="func-iterator-element_-equatable-index-of_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-equatable-index-of_">func index(<wbr>of:)</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-equatable-index-of_"><div class="p">
    <p>Returns the first index where the specified value appears in the
collection.</p>

<p>After using <code>index(of:)</code> to find the position of a particular element in
a collection, you can use it to access the element by subscripting. This
example shows how you can modify one of the names in an array of
students.</p>

<pre><code class="language-swift">var students = [&quot;Ben&quot;, &quot;Ivy&quot;, &quot;Jordell&quot;, &quot;Maxime&quot;]
if let i = students.index(of: &quot;Maxime&quot;) {
    students[i] = &quot;Max&quot;
}
print(students)
// Prints &quot;[&quot;Ben&quot;, &quot;Ivy&quot;, &quot;Jordell&quot;, &quot;Max&quot;]&quot;</code></pre>

<p><strong><code>element</code>:</strong>  An element to search for in the collection.
<strong>Returns:</strong> The first index where <code>element</code> is found. If <code>element</code> is not
  found in the collection, returns <code>nil</code>.</p>

<p><strong>See Also:</strong> <code>index(where:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func index(of element: Self.Iterator.Element) -&gt; Self.Index?</code>
    
    
</div></div>
</div>
<div class="declaration" id="func-iterator-element_-equatable-split_maxsplits_omittingemptysubsequences_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-equatable-split_maxsplits_omittingemptysubsequences_">func split(<wbr>_:<wbr>maxSplits:<wbr>omittingEmptySubsequences:)</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-equatable-split_maxsplits_omittingemptysubsequences_"><div class="p">
    <p>Returns the longest possible subsequences of the collection, in order,
around elements equal to the given element.</p>

<p>The resulting array consists of at most <code>maxSplits + 1</code> subsequences.
Elements that are used to split the collection are not returned as part
of any subsequence.</p>

<p>The following examples show the effects of the <code>maxSplits</code> and
<code>omittingEmptySubsequences</code> parameters when splitting a string at each
space character (&quot; &quot;). The first use of <code>split</code> returns each word that
was originally separated by one or more spaces.</p>

<pre><code class="language-swift">let line = &quot;BLANCHE:   I don&#39;t want realism. I want magic!&quot;
print(line.characters.split(separator: &quot; &quot;)
                     .map(String.init))
// Prints &quot;[&quot;BLANCHE:&quot;, &quot;I&quot;, &quot;don\&#39;t&quot;, &quot;want&quot;, &quot;realism.&quot;, &quot;I&quot;, &quot;want&quot;, &quot;magic!&quot;]&quot;</code></pre>

<p>The second example passes <code>1</code> for the <code>maxSplits</code> parameter, so the
original string is split just once, into two new strings.</p>

<pre><code class="language-swift">print(line.characters.split(separator: &quot; &quot;, maxSplits: 1)
                      .map(String.init))
// Prints &quot;[&quot;BLANCHE:&quot;, &quot;  I don\&#39;t want realism. I want magic!&quot;]&quot;</code></pre>

<p>The final example passes <code>false</code> for the <code>omittingEmptySubsequences</code>
parameter, so the returned array contains empty strings where spaces
were repeated.</p>

<pre><code class="language-swift">print(line.characters.split(separator: &quot; &quot;, omittingEmptySubsequences: false)
                      .map(String.init))
// Prints &quot;[&quot;BLANCHE:&quot;, &quot;&quot;, &quot;&quot;, &quot;I&quot;, &quot;don\&#39;t&quot;, &quot;want&quot;, &quot;realism.&quot;, &quot;I&quot;, &quot;want&quot;, &quot;magic!&quot;]&quot;</code></pre>

<p><strong>Parameters:</strong>
  <strong>separator:</strong> The element that should be split upon.
  <strong>maxSplits:</strong> The maximum number of times to split the collection, or
    one less than the number of subsequences to return. If
    <code>maxSplits + 1</code> subsequences are returned, the last one is a suffix
    of the original collection containing the remaining elements.
    <code>maxSplits</code> must be greater than or equal to zero. The default value
    is <code>Int.max</code>.
  <strong>omittingEmptySubsequences:</strong> If <code>false</code>, an empty subsequence is
    returned in the result for each consecutive pair of <code>separator</code>
    elements in the collection and for each instance of <code>separator</code> at
    the start or end of the collection. If <code>true</code>, only nonempty
    subsequences are returned. The default value is <code>true</code>.
<strong>Returns:</strong> An array of subsequences, split from this collection&#39;s
  elements.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func split(separator: Self.Iterator.Element, maxSplits: Int = default, omittingEmptySubsequences: Bool = default) -&gt; [Self.SubSequence]</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Collection/"><code>Collection</code></a>,    <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-iterator-element_-equatable-starts-with_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-equatable-starts-with_">func starts(<wbr>with:)</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-equatable-starts-with_"><div class="p">
    <p>Returns a Boolean value indicating whether the initial elements of the
sequence are the same as the elements in another sequence.</p>

<p>This example tests whether one countable range begins with the elements
of another countable range.</p>

<pre><code class="language-swift">let a = 1...3
let b = 1...10

print(b.starts(with: a))
// Prints &quot;true&quot;</code></pre>

<p>Passing an sequence with no elements or an empty collection as
<code>possiblePrefix</code> always results in <code>true</code>.</p>

<pre><code class="language-swift">print(b.starts(with: []))
// Prints &quot;true&quot;</code></pre>

<p><strong><code>possiblePrefix</code>:</strong>  A sequence to compare to this sequence.
<strong>Returns:</strong> <code>true</code> if the initial elements of the sequence are the same as
  the elements of <code>possiblePrefix</code>; otherwise, <code>false</code>. If
  <code>possiblePrefix</code> has no elements, the return value is <code>true</code>.</p>

<p><strong>See Also:</strong> <code>starts(with:by:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func starts&lt;PossiblePrefix where PossiblePrefix : Sequence, PossiblePrefix.Iterator.Element == Iterator.Element&gt;(with possiblePrefix: PossiblePrefix) -&gt; Bool</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>





<h4>Where Iterator.Element : Sequence</h4>




<div class="declaration inherited" id="func-iterator-element_-sequence-joined">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-sequence-joined">func joined()</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-sequence-joined"><div class="p">
    <p>Returns the elements of this sequence of sequences, concatenated.</p>

<p>In this example, an array of three ranges is flattened so that the
elements of each range can be iterated in turn.</p>

<pre><code class="language-swift">let ranges = [0..&lt;3, 8..&lt;10, 15..&lt;17]

// A for-in loop over &#39;ranges&#39; accesses each range:
for range in ranges {
  print(range)
}
// Prints &quot;0..&lt;3&quot;
// Prints &quot;8..&lt;10&quot;
// Prints &quot;15..&lt;17&quot;

// Use &#39;joined()&#39; to access each element of each range:
for index in ranges.joined() {
    print(index, terminator: &quot; &quot;)
}
// Prints: &quot;0 1 2 8 9 15 16&quot;</code></pre>

<p><strong>Returns:</strong> A flattened view of the elements of this
  sequence of sequences.</p>

<p><strong>See Also:</strong> <code>flatMap(_:)</code>, <code>joined(separator:)</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func joined() -&gt; FlattenSequence&lt;Self&gt;</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-iterator-element_-sequence-joined_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element_-sequence-joined_">func joined(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-iterator-element_-sequence-joined_"><div class="p">
    <p>Returns the concatenated elements of this sequence of sequences,
inserting the given separator between each element.</p>

<p>This example shows how an array of <code>[Int]</code> instances can be joined, using
another <code>[Int]</code> instance as the separator:</p>

<pre><code class="language-swift">let nestedNumbers = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
let joined = nestedNumbers.joined(separator: [-1, -2])
print(Array(joined))
// Prints &quot;[1, 2, 3, -1, -2, 4, 5, 6, -1, -2, 7, 8, 9]&quot;</code></pre>

<p><strong><code>separator</code>:</strong>  A sequence to insert between each of this
  sequence&#39;s elements.
<strong>Returns:</strong> The joined sequence of elements.</p>

<p><strong>See Also:</strong> <code>joined()</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">func joined&lt;Separator : Sequence where Separator.Iterator.Element == Iterator.Element.Iterator.Element&gt;(separator: Separator) -&gt; JoinedSequence&lt;Self&gt;</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>





<h4>Where Iterator.Element == String</h4>




<div class="declaration inherited" id="func-iterator-element-string-joined_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-iterator-element-string-joined_">func joined(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-iterator-element-string-joined_"><div class="p">
    <p>Returns a new string by concatenating the elements of the sequence,
adding the given separator between each element.</p>

<p>The following example shows how an array of strings can be joined to a
single, comma-separated string:</p>

<pre><code class="language-swift">let cast = [&quot;Vivien&quot;, &quot;Marlon&quot;, &quot;Kim&quot;, &quot;Karl&quot;]
let list = cast.joined(separator: &quot;, &quot;)
print(list)
// Prints &quot;Vivien, Marlon, Kim, Karl&quot;</code></pre>

<p><strong><code>separator</code>:</strong>  A string to insert between each of the elements
  in this sequence. The default separator is an empty string.
<strong>Returns:</strong> A single, concatenated string.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func joined(separator: String = default) -&gt; String</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>





<h4>Where Self : LazyCollectionProtocol</h4>


<div class="declaration" id="self_-lazycollectionprotocol-var-lazy_-self">
<a class="toggle-link" data-toggle="collapse" href="#comment-self_-lazycollectionprotocol-var-lazy_-self">var lazy: Self</a><div class="comment collapse" id="comment-self_-lazycollectionprotocol-var-lazy_-self"><div class="p">
    <p>Identical to <code>self</code>.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var lazy: Self { get }</code>

    </div></div>
</div>







<h4>Where SubSequence : Sequence, SubSequence.Iterator.Element == Iterator.Element, SubSequence.SubSequence == SubSequence</h4>




<div class="declaration inherited" id="func-subsequence_-sequence-subsequence-iterator-element-iterator-element-subsequence-subsequence-subsequence-dropfirst_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-subsequence_-sequence-subsequence-iterator-element-iterator-element-subsequence-subsequence-subsequence-dropfirst_">func dropFirst(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-subsequence_-sequence-subsequence-iterator-element-iterator-element-subsequence-subsequence-subsequence-dropfirst_"><div class="p">
    <p>Returns a subsequence containing all but the given number of initial
elements.</p>

<p>If the number of elements to drop exceeds the number of elements in
the sequence, the result is an empty subsequence.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.dropFirst(2))
// Prints &quot;[3, 4, 5]&quot;
print(numbers.dropFirst(10))
// Prints &quot;[]&quot;</code></pre>

<p><strong><code>n</code>:</strong>  The number of elements to drop from the beginning of
  the sequence. <code>n</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence starting after the specified number of
  elements.</p>

<p><strong>Complexity:</strong> O(1).</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func dropFirst(_ n: Int) -&gt; AnySequence&lt;Self.Iterator.Element&gt;</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-subsequence_-sequence-subsequence-iterator-element-iterator-element-subsequence-subsequence-subsequence-droplast_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-subsequence_-sequence-subsequence-iterator-element-iterator-element-subsequence-subsequence-subsequence-droplast_">func dropLast(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-subsequence_-sequence-subsequence-iterator-element-iterator-element-subsequence-subsequence-subsequence-droplast_"><div class="p">
    <p>Returns a subsequence containing all but the given number of final
elements.</p>

<p>The sequence must be finite. If the number of elements to drop exceeds
the number of elements in the sequence, the result is an empty
subsequence.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.dropLast(2))
// Prints &quot;[1, 2, 3]&quot;
print(numbers.dropLast(10))
// Prints &quot;[]&quot;</code></pre>

<p><strong><code>n</code>:</strong>  The number of elements to drop off the end of the
  sequence. <code>n</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence leaving off the specified number of elements.</p>

<p><strong>Complexity:</strong> O(<em>n</em>), where <em>n</em> is the length of the sequence.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func dropLast(_ n: Int) -&gt; AnySequence&lt;Self.Iterator.Element&gt;</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>
<div class="declaration inherited" id="func-subsequence_-sequence-subsequence-iterator-element-iterator-element-subsequence-subsequence-subsequence-prefix_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-subsequence_-sequence-subsequence-iterator-element-iterator-element-subsequence-subsequence-subsequence-prefix_">func prefix(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-subsequence_-sequence-subsequence-iterator-element-iterator-element-subsequence-subsequence-subsequence-prefix_"><div class="p">
    <p>Returns a subsequence, up to the specified maximum length, containing the
initial elements of the sequence.</p>

<p>If the maximum length exceeds the number of elements in the sequence,
the result contains all the elements in the sequence.</p>

<pre><code class="language-swift">let numbers = [1, 2, 3, 4, 5]
print(numbers.prefix(2))
// Prints &quot;[1, 2]&quot;
print(numbers.prefix(10))
// Prints &quot;[1, 2, 3, 4, 5]&quot;</code></pre>

<p><strong><code>maxLength</code>:</strong>  The maximum number of elements to return. The
  value of <code>maxLength</code> must be greater than or equal to zero.
<strong>Returns:</strong> A subsequence starting at the beginning of this sequence
  with at most <code>maxLength</code> elements.</p>

<p><strong>Complexity:</strong> O(1)</p>

    <h4>Declaration</h4>    
    <code class="language-swift">func prefix(_ maxLength: Int) -&gt; AnySequence&lt;Self.Iterator.Element&gt;</code>
    
        <h4>Declared In</h4>
        <a href="../../protocol/Sequence/"><code>Sequence</code></a>    
</div></div>
</div>





<h4>Where SubSequence == Self</h4>




<div class="declaration" id="func-subsequence-self-popfirst">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-subsequence-self-popfirst">mutating func popFirst()</a>
        
<div class="comment collapse" id="comment-func-subsequence-self-popfirst"><div class="p">
    <p>Removes and returns the first element of the collection.</p>

<p><strong>Returns:</strong> The first element of the collection if the collection is
  not empty; otherwise, <code>nil</code>.</p>

<p><strong>Complexity:</strong> O(1)</p>

    <h4>Declaration</h4>    
    <code class="language-swift">mutating func popFirst() -&gt; Self.Iterator.Element?</code>
    
    
</div></div>
</div>
<div class="declaration" id="func-subsequence-self-removefirst">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-subsequence-self-removefirst">mutating func removeFirst()</a>
        
<div class="comment collapse" id="comment-func-subsequence-self-removefirst"><div class="p">
    <p>Removes and returns the first element of the collection.</p>

<p>The collection must not be empty.</p>

<p><strong>Returns:</strong> The first element of the collection.</p>

<p><strong>Complexity:</strong> O(1)
<strong>See Also:</strong> <code>popFirst()</code></p>

    <h4>Declaration</h4>    
    <code class="language-swift">mutating func removeFirst() -&gt; Self.Iterator.Element</code>
    
    
</div></div>
</div>
<div class="declaration" id="func-subsequence-self-removefirst_">
<a class="toggle-link" data-toggle="collapse" href="#comment-func-subsequence-self-removefirst_">mutating func removeFirst(<wbr>_:)</a>
        
<div class="comment collapse" id="comment-func-subsequence-self-removefirst_"><div class="p">
    <p>Removes the specified number of elements from the beginning of the
collection.</p>

<p><strong><code>n</code>:</strong>  The number of elements to remove. <code>n</code> must be greater than
  or equal to zero, and must be less than or equal to the number of
  elements in the collection.</p>

<p><strong>Complexity:</strong> O(1) if the collection conforms to
  <code>RandomAccessCollection</code>; otherwise, O(<em>n</em>).</p>

    <h4>Declaration</h4>    
    <code class="language-swift">mutating func removeFirst(_ n: Int)</code>
    
    
</div></div>
</div>





<h4>Where SubSequence == Slice<Self></h4>



<div class="declaration" id="subscript-subsequence-slice-self-subscript_-range-self-index">
<a class="toggle-link" data-toggle="collapse" href="#comment-subscript-subsequence-slice-self-subscript_-range-self-index">subscript(_: Range&lt;Self.Index&gt;)</a>
<div class="comment collapse" id="comment-subscript-subsequence-slice-self-subscript_-range-self-index"><div class="p">
    <p>Accesses a contiguous subrange of the collection&#39;s elements.</p>

<p>The accessed slice uses the same indices for the same elements as the
original collection uses. Always use the slice&#39;s <code>startIndex</code> property
instead of assuming that its indices start at a particular value.</p>

<p>This example demonstrates getting a slice of an array of strings, finding
the index of one of the strings in the slice, and then using that index
in the original array.</p>

<pre><code class="language-swift">let streets = [&quot;Adams&quot;, &quot;Bryant&quot;, &quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]
let streetsSlice = streets[2 ..&lt; streets.endIndex]
print(streetsSlice)
// Prints &quot;[&quot;Channing&quot;, &quot;Douglas&quot;, &quot;Evarts&quot;]&quot;

let index = streetsSlice.index(of: &quot;Evarts&quot;)    // 4
print(streets[index!])
// Prints &quot;Evarts&quot;</code></pre>

<p><strong><code>bounds</code>:</strong>  A range of the collection&#39;s indices. The bounds of
  the range must be valid indices of the collection.</p>

    <h4>Declaration</h4>    
    <code class="language-swift">subscript(bounds: Range&lt;Self.Index&gt;) -&gt; Slice&lt;Self&gt; { get }</code>
    
    
</div></div>
</div>




